David Witte - Academia.edu (original) (raw)

Papers by David Witte

Research paper thumbnail of Sources of variability: A College of American Pathologists Therapeutic Drug Monitoring Survey Study

Archives of Pathology & Laboratory Medicine, 2001

○ Objective.-To determine the magnitudes and sources of analytic variation in testing for therape... more ○ Objective.-To determine the magnitudes and sources of analytic variation in testing for therapeutic drugs. Specifically, among laboratories using the same analytic method, to compare the within-laboratory variation (including both short- and long-term variation) with the between-laboratory variation. Design.-Four identical challenges were prepared from a lyophilized pool of spiked sera and were sent in pairs 4 months apart to laboratories participating in a nationwide proficiency-testing program. For each of 25 drugs, the variability in reported results from laboratories using the same method was investigated using nested analysis of variance. Setting.-The first 2 mailings of the College of American Pathologists Therapeutic Drug Monitoring Survey, 1996, sets Z and ZM. Main Outcome Measures.-For each drug, total variance was partitioned into within- and between-laboratory components for common methods. The within-laboratory component was further partitioned into short- and long-ter...

Research paper thumbnail of Predicting Bone Marrow Iron Stores in Anemic Patients in a Community Hospital Using Ferritin and Erythrocyte Sedimentation Rate

American Journal of Clinical Pathology, 1988

Forty-three consecutive cases from a community hospital with concomitant bone marrow iron stain, ... more Forty-three consecutive cases from a community hospital with concomitant bone marrow iron stain, serum ferritin, and erythrocyte sedimentation rate (ESR) were reviewed. Cases were classified as iron present or absent by the bone marrow iron stain. A two-dimensional linear graphic relationship between ferritin and ESR correctly identified six of nine iron-deficient patients and 32 of 34 iron-present patients. Four cases yielded indeterminate results. One complex iron-deficient case was incorrectly classified. This graphic method developed with data from tertiary care patients was correct in 88.4% of cases, incorrect in 2.3%, and indeterminate in 9.3%. When absent iron stores were graphically predicted, the predictive value was 100%. When iron deficiency was graphically excluded, the predictive value was 97%. The authors conclude the graphic method is useful in a community hospital practice for the confirmation or exclusion of iron deficiency.

Research paper thumbnail of State of the Art in Clinical and Anatomic Pathology

N Pathologists have long served as custodians of human biospecimens collected for diagnostic purp... more N Pathologists have long served as custodians of human biospecimens collected for diagnostic purposes. Rapid advancements in diagnostic technologies require that pathologists change their practices to optimize patient care. The proper handling of biospecimens creates opportunities for pathologists to improve their diagnoses while assessing prognosis and treatment. In addition, the growing need for high-quality biorepositories represents an opportunity for community pathologists to strengthen their role within the health care team, ensuring that clinical care is not compromised while facilitating research. This article provides a resource to community pathologists learning how to create high-quality biorepositories and participating in emerging opportunities in the biorepository field. While a variety of topics are covered to provide breadth of information, the intent is to facilitate a level of understanding that permits community pathologists to make more informed choices in identi...

Research paper thumbnail of An Evaluation of Analytic Goals for Assays of Drugs

Archives of Pathology & Laboratory Medicine, 2001

Objective.—To determine if the levels of imprecision of the commonly used analytic methods for dr... more Objective.—To determine if the levels of imprecision of the commonly used analytic methods for drug measurements are suitable for long-term therapeutic drug monitoring. Design.—In 1996, 4 identical lyophilized samples (2 in the first mailing and 2 in the second mailing 4 months later) were sent to laboratories participating in a nationwide proficiency testing program. Similarly, in 1999, replicates from a liquid pool of spiked sera were mailed 3 times, 4 months apart, to participating laboratories. For each of 11 drugs regulated under the Clinical Laboratory Improvement Amendments of 1988 and 1 metabolite, the total variance for each method was partitioned into within- and between-laboratory components. The total within-laboratory and the total survey coefficients of variation (CVs) for each method were then compared with the “acceptable” precision criteria of Glick, Burnett, and Fraser for each drug. Setting.—The first 2 mailings of the College of American Pathologists Therapeutic ...

Research paper thumbnail of EnzymicInhibitionAssayfor M#{234}thotrexate with a DiscreteAnalyzer,the ABA-100

We adapted an inhibition assay for methotrexate, involving dihydrofolate reductase from bovine li... more We adapted an inhibition assay for methotrexate, involving dihydrofolate reductase from bovine liver, for use with a discrete analyzer (the ABA-100). The analyzer waused both for dilution and a 5-mm pre-incubation of the sample with NADPH-enzyme reagent, and for the assay itself. The standard curve was linear between 10 and 120 tg/L. Without pre-incubation the standard curve was nonlinear. The presence of albumin in the NADPH-enzyme reagent enhanced both enzyme activity and stability. Within-run precision (CV) was 2.0% (n = 24), run-to-run precision 7.1% (n = 49). Results obtained on patients’ samples (29 sera, 15 urines, 18 cerebrospinal fluids) by the present method and a radioimmunoassay method did not differ statisti#{243}ally (p >0.05) when the paired data were analyzed by use of the sign test and Wilcoxon’s ranked sign test.

Research paper thumbnail of Redesigned Proficiency Testing Materials Improve Survey Outcomes for Prostate-Specific Antigen

Archives of Pathology & Laboratory Medicine, 2000

Context.—Large disparities in prostate-specific antigen (PSA) results from different assays have ... more Context.—Large disparities in prostate-specific antigen (PSA) results from different assays have been observed in the College of American Pathologists (CAP) Ligand Assay Survey, with interassay results varying severalfold. Survey specimens are predominately composed of free PSA and do not reflect the composition of typical patient specimens. Objectives.—To characterize a pilot material developed for CAP in which pooled sera samples were spiked with purified PSA and α1-antichymotrypsin–bound PSA at targeted concentrations and to compare it to CAP survey and reference materials. Design.—CAP survey, reference, and pilot materials were analyzed using 10 total PSA and 7 free PSA assays. These assays included Food and Drug Administration–approved assays and assays for research use only. Results.—Variability among the 10 total PSA methods was greatest for the 1997 ligand survey material (CV range, 56%–65%) followed by the pilot material (CV range, 10%–29%) and the reference material (CV ra...

Research paper thumbnail of Frequency of Unacceptable Results in Point-of-Care Testing

Archives of Pathology & Laboratory Medicine, 1999

K ilgore and associates 1 show how the rich source of information available in the laboratory can... more K ilgore and associates 1 show how the rich source of information available in the laboratory can be used to improve care processes. The ''naturally concurrent'' results from laboratory and point-of-care hematocrit measurements helped improve quality, and this concurrence exemplifies the real-time science of laboratory medicine. This article stimulates the search for similar improvement opportunities and suggests a practical research agenda. Kilgore et al did not differentiate common cause and special cause sources of variation. 2 Common cause variation, usually modeled with the gaussian distribution, suggests that results beyond 3 SDs occur at a frequency of about 0.27%, or 2700 parts per million (ppm). Further, 4 SDs yield 63 ppm, 5 SDs yield 0.6 ppm, and 6 SDs yield 0.002 ppm, outlier rates in a gaussian distribution with no bias in the midpoint. Special cause variation is distinct from common cause and is believed to be attributable to unexpected sources of variation and is not modeled by the gaussian distribution. 2 The figure presented by Kilgore et al suggests frequent special cause outliers in January and infrequent special cause variation plus perhaps smaller common cause variation in April. The authors defined a clinically significant difference as 5 hemat

Research paper thumbnail of Single-stage automated assay for heparin

Clinical Chemistry, 1982

We have developed a single-stage assay for heparin, using reagents modified from the two-stage Da... more We have developed a single-stage assay for heparin, using reagents modified from the two-stage Dade Protopath heparin synthetic substrate assay. The single-stage assay involves simultaneous mixing of a plasma sample, an antithrombin III source, alpha-thrombin, and the alpha-thrombin fluorogenic substrate. The synthetic substrate, antithrombin III, and heparin-antithrombin III complex compete for the alpha-thrombin active site. The alpha-thrombin is inactivated by the heparin-antithrombin complex while substrate is being hydrolyzed, so that total product formation decreases with heparin concentration. Day-to-day CV was 9.3% at a heparin concentration of 246 USP units/L. Comparison of results of the single-stage heparin assay with those of a two-stage esterolytic assay yielded the linear regression equation: esterolytic = 0.834 (single-stage)--7 USP units/L (r = 0.94, n = 47). Bilirubin interfered with the single-stage assay, resulting in an apparent increase in sample heparin concent...

Research paper thumbnail of Can serum ferritin be effectively interpreted in the presence of the acute-phase response?

Research paper thumbnail of Errors, mistakes, blunders, outliers, or unacceptable results: how many?

Clinical Chemistry, 1997

We have studied 219 353 individual clinical chemistry results obtained in methods comparison stud... more We have studied 219 353 individual clinical chemistry results obtained in methods comparison studies. Each result was prospectively compared with its replicate, comparative, or repeat value to identify differences from expected values. Unacceptable results were defined as differing from the expected values by ≤7 SDs or CVs. We believe these differences represent special-cause variation and should be expressed as unacceptable rates per million results (ppm). We observed 447 ppm unacceptables: 196 ppm in control samples and 251 ppm in patients’ samples. Results judged likely to alter patient care occurred at a rate of 41 ppm. To better understand the magnitude of these rates, we compared these results with reports of error rates in HIV testing and the airline industry. The measurements reported were made for the purpose of quality improvement, not judgment or discovery. The significance of these findings for laboratorians, manufacturers, and regulators is discussed.

Research paper thumbnail of Esterolytic method for determination of heparin in plasma

Clinical Chemistry, 1981

This assay for heparin is based on the heparin-accelerated rate of alpha-thrombin III. The rate o... more This assay for heparin is based on the heparin-accelerated rate of alpha-thrombin III. The rate or product formation from the residual active thrombin is inversely proportional to plasma heparin content. The assay can be performed manually, but our results were obtained with a discrete analyzer, the ABA-100. The assay is insensitive to concentrations of antithrombin III in plasma. Precision studies gave CVs of less than 10%. This assay was compared to the Dade Protopath heparin assay and a correlation coefficient of 0.90 was obtained (n = 62). The correlation between activated partial thromboplastin times and heparin concentrations (r = 0.67) was calculated frm results on 78 plasma specimens from 10 patients.

Research paper thumbnail of Panel discussion: how to monitor and minimize variation and mistakes

Research paper thumbnail of Effects of bilirubin on detection of hydrogen peroxide by use of peroxidase

Clinical Chemistry, 1978

Bilitubin interferes with the quantitation of hydrogen peroxide in reagent systems in which perox... more Bilitubin interferes with the quantitation of hydrogen peroxide in reagent systems in which peroxidase is used. Difference spectra suggest that this interference is a combination of chemical and spectral effects. The data presented are most consistent with the following interpretation: (a) bilirubin destroys part of the reactive intermediate formed in the peroxidase reaction and thus decreases the amount of chromophore formed and (b) the spectra for bilirubin and the chromaphore overlap, which also affects the results. The relevance of these results to reagent design and laboratory quality control are discussed.

Research paper thumbnail of Enzymic inhibition assay for methotrexate with a discrete analyzer, the ABA-100

Clinical Chemistry, 1980

We adapted an inhibition assay for methotrexate, involving dihydrofolate reductase from bovine li... more We adapted an inhibition assay for methotrexate, involving dihydrofolate reductase from bovine liver, for use with a discrete analyzer (the ABA-100). The analyzer was used both for dilution and a 5-min pre-incubation of the sample with NADPH--enzyme reagent, and for the assay itself. The standard curve was linear between 10 and 120 microgram/L. Without pre-incubation the standard curve was nonlinear. The presence of albumin in the NADPH--enzyme reagent enhanced both enzyme activity and stability. Within-run precision (CV) was 2.0% (n = 24), run-to-run precision 7.1% (n = 49). Results obtained on patients' samples (29 sera, 15 urines, 18 cerebrospinal fluids) by the present method and a radioimmunoassay method did not differ statistically (p greater than 0.05) when the paired data were analyzed by use of the sign test and Wilcoxon's ranked sign test.

Research paper thumbnail of Serum uric acid determined by reversed-phase liquid chromatography with spectrophotometric detection

Clinical Chemistry, 1978

We describe a method for determining uric acid in serum by reversed-phase liquid chromatography w... more We describe a method for determining uric acid in serum by reversed-phase liquid chromatography with spectrophotometric detection at 280 nm. Serum, 100 ul is mixed with 100 u1 of a solution containing, per liter, 70 ml of acetonitrile in sodium acetate (20 mmol/Iiter, pH 4.0) and 500 mg of the internal standard, adenine. The mixture is allowed to stand in an ice bath for 3 mm, then centrifuged. A 7.5tl portion of the supernate is chromatographed on a “ Bondpak C18” column, with a 35 mI/liter solution of acetonitrile in sodium acetate (10 mmol/liter, pH 4.0) as the mobile phase. For 10 runs of duplicates, the within-run CV was 1.2% and the day-to-day CV (10 days) was 2.5% for a uric acid concentration of 53 mg/liter. Sera from 100 patients were analyzed for uric acid by the proposed method, a continuous-flow (SMA 12/60) method, and a uricase method; mean values for the 100 sera were 64, 71, and 64 mg/liter, respectively. Correlations were as follows: r = 0.987 for proposed method vs. SMA 12/60 and r = 0.997 for proposed method vs. the uricase method. The proposed method is sensitive and specific and we think it will be useful for evaluating other i.ilc acid methods for interference and specificity.

Research paper thumbnail of Presence of creatine kinase BB isoenzyme in some patients with prostatic carcinoma

Clinical Chemistry, 1977

We have observed creatine kinase isoenzyme BB in the sera of nine of 19 patients with Stage D car... more We have observed creatine kinase isoenzyme BB in the sera of nine of 19 patients with Stage D carcinoma of the prostate. Its presence does not seem to correlate with acid phosphatase activity in serum or the presence of bone metastases as indicated by increased alkaline phosphatase activity in serum. Only three of the nine patients with BB isoenzyme activity detectable in their serum had abnormal values for total creatine kinase activity, but all had abnormal values for alkaline and acid phosphatase activity. All 10 patients with no BB isoenzyme detectable had abnormal acid phosphatase values; however, only seven had increased alkaline phosphatase values and only one had increased creatine kinase activity.

Research paper thumbnail of Kinetic determination of serum lipase activity with the Abbott ABA-100

Clinical Chemistry, 1976

A turbidimetric procedure for lipase has been adapted for use on the Abbott Bichromatic Analyzer ... more A turbidimetric procedure for lipase has been adapted for use on the Abbott Bichromatic Analyzer (ABA-100). The method is rapid and results compared well with those by the more traditional method of Cherry and Crandall [Am. J. Physiol. 100, 266 (1932)]. Advantages of this method include shorter incubation time (2 min), smaller sample size (50 mul), neglible interference from bilirubin, and greater dynamic range (to eightfold normal).

Research paper thumbnail of Medically relevant laboratory-performance goals: a listing of the complexities and a call for action

Clinical Chemistry, 1993

This 1992 Clinical Chemistry Forum asks if accuracy and precision goals for the laboratory can be... more This 1992 Clinical Chemistry Forum asks if accuracy and precision goals for the laboratory can be specified by reference to medical requirements, which are a function of the total laboratory testing process as well as the needs of patients, clinicians, and societal institutions. Furthermore, medical decisions and decisions about medical requirements must be made in situations of uncertainty and thus are subject to predictable cognitive errors. The interaction of all these factors must be considered by patients, laboratorians, and clinicians to identify practical and effective performance goals. Pathologists and clinical chemists are uniquely trained to identify thoughtful clinicians who are knowledgeable in quantitative judgment to participate in this goal-setting endeavor. It is time for these parties to accumulate the available data and engage in the synthesis of effective performance goals.

Research paper thumbnail of Wellness Testing: Design and Experience of an Established Program

Clinics in Laboratory Medicine, 1993

Research paper thumbnail of Prediction of Bone Marrow Iron Findings from Tests Performed on Peripheral Blood

American Journal of Clinical Pathology, 1986

After evaluating multiple tests, the authors have devised a scheme to predict bone marrow iron fi... more After evaluating multiple tests, the authors have devised a scheme to predict bone marrow iron findings from tests performed on peripheral blood. They examined bone marrows from 97 consecutive patients with anemia who were divided into five marrow morphologic groups: (1) iron deficiency; (2) anemia of chronic disease; (3) abnormal sideroblasts; (4) ring sideroblasts; and (5) other. Tests of peripheral blood included hemoglobin, hematocrit, red blood cell count and red blood cell indices, reticulocyte count, sedimentation rate or zetacrit, ferritin, iron, iron binding capacity, free erythrocyte protoporphyrin, and tests of hepatic and renal function. Cluster analysis, multidimensional scaling, and logistic discriminant analysis were used to derive a graph of serum ferritin with the sedimentation rate, allowing accurate confirmation or exclusion of iron deficiency in most patients. Percent saturation of serum transferrin and serum ferritin allowed identification of only 50 percent of patients with abnormal or ring sideroblasts while excluding 100 percent of patients without abnormal or ring sideroblasts. In three years of follow-up, two of 19 patients with abnormal or ring sideroblast have developed the dysmyelopoietic syndrome or ANLL, respectively. With the aid of the two parameter graphs described, the authors believe the differential diagnosis of the hypoproliferative anemias relating to iron metabolism can frequently be made without examination of the bone marrow.

Research paper thumbnail of Sources of variability: A College of American Pathologists Therapeutic Drug Monitoring Survey Study

Archives of Pathology & Laboratory Medicine, 2001

○ Objective.-To determine the magnitudes and sources of analytic variation in testing for therape... more ○ Objective.-To determine the magnitudes and sources of analytic variation in testing for therapeutic drugs. Specifically, among laboratories using the same analytic method, to compare the within-laboratory variation (including both short- and long-term variation) with the between-laboratory variation. Design.-Four identical challenges were prepared from a lyophilized pool of spiked sera and were sent in pairs 4 months apart to laboratories participating in a nationwide proficiency-testing program. For each of 25 drugs, the variability in reported results from laboratories using the same method was investigated using nested analysis of variance. Setting.-The first 2 mailings of the College of American Pathologists Therapeutic Drug Monitoring Survey, 1996, sets Z and ZM. Main Outcome Measures.-For each drug, total variance was partitioned into within- and between-laboratory components for common methods. The within-laboratory component was further partitioned into short- and long-ter...

Research paper thumbnail of Predicting Bone Marrow Iron Stores in Anemic Patients in a Community Hospital Using Ferritin and Erythrocyte Sedimentation Rate

American Journal of Clinical Pathology, 1988

Forty-three consecutive cases from a community hospital with concomitant bone marrow iron stain, ... more Forty-three consecutive cases from a community hospital with concomitant bone marrow iron stain, serum ferritin, and erythrocyte sedimentation rate (ESR) were reviewed. Cases were classified as iron present or absent by the bone marrow iron stain. A two-dimensional linear graphic relationship between ferritin and ESR correctly identified six of nine iron-deficient patients and 32 of 34 iron-present patients. Four cases yielded indeterminate results. One complex iron-deficient case was incorrectly classified. This graphic method developed with data from tertiary care patients was correct in 88.4% of cases, incorrect in 2.3%, and indeterminate in 9.3%. When absent iron stores were graphically predicted, the predictive value was 100%. When iron deficiency was graphically excluded, the predictive value was 97%. The authors conclude the graphic method is useful in a community hospital practice for the confirmation or exclusion of iron deficiency.

Research paper thumbnail of State of the Art in Clinical and Anatomic Pathology

N Pathologists have long served as custodians of human biospecimens collected for diagnostic purp... more N Pathologists have long served as custodians of human biospecimens collected for diagnostic purposes. Rapid advancements in diagnostic technologies require that pathologists change their practices to optimize patient care. The proper handling of biospecimens creates opportunities for pathologists to improve their diagnoses while assessing prognosis and treatment. In addition, the growing need for high-quality biorepositories represents an opportunity for community pathologists to strengthen their role within the health care team, ensuring that clinical care is not compromised while facilitating research. This article provides a resource to community pathologists learning how to create high-quality biorepositories and participating in emerging opportunities in the biorepository field. While a variety of topics are covered to provide breadth of information, the intent is to facilitate a level of understanding that permits community pathologists to make more informed choices in identi...

Research paper thumbnail of An Evaluation of Analytic Goals for Assays of Drugs

Archives of Pathology & Laboratory Medicine, 2001

Objective.—To determine if the levels of imprecision of the commonly used analytic methods for dr... more Objective.—To determine if the levels of imprecision of the commonly used analytic methods for drug measurements are suitable for long-term therapeutic drug monitoring. Design.—In 1996, 4 identical lyophilized samples (2 in the first mailing and 2 in the second mailing 4 months later) were sent to laboratories participating in a nationwide proficiency testing program. Similarly, in 1999, replicates from a liquid pool of spiked sera were mailed 3 times, 4 months apart, to participating laboratories. For each of 11 drugs regulated under the Clinical Laboratory Improvement Amendments of 1988 and 1 metabolite, the total variance for each method was partitioned into within- and between-laboratory components. The total within-laboratory and the total survey coefficients of variation (CVs) for each method were then compared with the “acceptable” precision criteria of Glick, Burnett, and Fraser for each drug. Setting.—The first 2 mailings of the College of American Pathologists Therapeutic ...

Research paper thumbnail of EnzymicInhibitionAssayfor M#{234}thotrexate with a DiscreteAnalyzer,the ABA-100

We adapted an inhibition assay for methotrexate, involving dihydrofolate reductase from bovine li... more We adapted an inhibition assay for methotrexate, involving dihydrofolate reductase from bovine liver, for use with a discrete analyzer (the ABA-100). The analyzer waused both for dilution and a 5-mm pre-incubation of the sample with NADPH-enzyme reagent, and for the assay itself. The standard curve was linear between 10 and 120 tg/L. Without pre-incubation the standard curve was nonlinear. The presence of albumin in the NADPH-enzyme reagent enhanced both enzyme activity and stability. Within-run precision (CV) was 2.0% (n = 24), run-to-run precision 7.1% (n = 49). Results obtained on patients’ samples (29 sera, 15 urines, 18 cerebrospinal fluids) by the present method and a radioimmunoassay method did not differ statisti#{243}ally (p >0.05) when the paired data were analyzed by use of the sign test and Wilcoxon’s ranked sign test.

Research paper thumbnail of Redesigned Proficiency Testing Materials Improve Survey Outcomes for Prostate-Specific Antigen

Archives of Pathology & Laboratory Medicine, 2000

Context.—Large disparities in prostate-specific antigen (PSA) results from different assays have ... more Context.—Large disparities in prostate-specific antigen (PSA) results from different assays have been observed in the College of American Pathologists (CAP) Ligand Assay Survey, with interassay results varying severalfold. Survey specimens are predominately composed of free PSA and do not reflect the composition of typical patient specimens. Objectives.—To characterize a pilot material developed for CAP in which pooled sera samples were spiked with purified PSA and α1-antichymotrypsin–bound PSA at targeted concentrations and to compare it to CAP survey and reference materials. Design.—CAP survey, reference, and pilot materials were analyzed using 10 total PSA and 7 free PSA assays. These assays included Food and Drug Administration–approved assays and assays for research use only. Results.—Variability among the 10 total PSA methods was greatest for the 1997 ligand survey material (CV range, 56%–65%) followed by the pilot material (CV range, 10%–29%) and the reference material (CV ra...

Research paper thumbnail of Frequency of Unacceptable Results in Point-of-Care Testing

Archives of Pathology & Laboratory Medicine, 1999

K ilgore and associates 1 show how the rich source of information available in the laboratory can... more K ilgore and associates 1 show how the rich source of information available in the laboratory can be used to improve care processes. The ''naturally concurrent'' results from laboratory and point-of-care hematocrit measurements helped improve quality, and this concurrence exemplifies the real-time science of laboratory medicine. This article stimulates the search for similar improvement opportunities and suggests a practical research agenda. Kilgore et al did not differentiate common cause and special cause sources of variation. 2 Common cause variation, usually modeled with the gaussian distribution, suggests that results beyond 3 SDs occur at a frequency of about 0.27%, or 2700 parts per million (ppm). Further, 4 SDs yield 63 ppm, 5 SDs yield 0.6 ppm, and 6 SDs yield 0.002 ppm, outlier rates in a gaussian distribution with no bias in the midpoint. Special cause variation is distinct from common cause and is believed to be attributable to unexpected sources of variation and is not modeled by the gaussian distribution. 2 The figure presented by Kilgore et al suggests frequent special cause outliers in January and infrequent special cause variation plus perhaps smaller common cause variation in April. The authors defined a clinically significant difference as 5 hemat

Research paper thumbnail of Single-stage automated assay for heparin

Clinical Chemistry, 1982

We have developed a single-stage assay for heparin, using reagents modified from the two-stage Da... more We have developed a single-stage assay for heparin, using reagents modified from the two-stage Dade Protopath heparin synthetic substrate assay. The single-stage assay involves simultaneous mixing of a plasma sample, an antithrombin III source, alpha-thrombin, and the alpha-thrombin fluorogenic substrate. The synthetic substrate, antithrombin III, and heparin-antithrombin III complex compete for the alpha-thrombin active site. The alpha-thrombin is inactivated by the heparin-antithrombin complex while substrate is being hydrolyzed, so that total product formation decreases with heparin concentration. Day-to-day CV was 9.3% at a heparin concentration of 246 USP units/L. Comparison of results of the single-stage heparin assay with those of a two-stage esterolytic assay yielded the linear regression equation: esterolytic = 0.834 (single-stage)--7 USP units/L (r = 0.94, n = 47). Bilirubin interfered with the single-stage assay, resulting in an apparent increase in sample heparin concent...

Research paper thumbnail of Can serum ferritin be effectively interpreted in the presence of the acute-phase response?

Research paper thumbnail of Errors, mistakes, blunders, outliers, or unacceptable results: how many?

Clinical Chemistry, 1997

We have studied 219 353 individual clinical chemistry results obtained in methods comparison stud... more We have studied 219 353 individual clinical chemistry results obtained in methods comparison studies. Each result was prospectively compared with its replicate, comparative, or repeat value to identify differences from expected values. Unacceptable results were defined as differing from the expected values by ≤7 SDs or CVs. We believe these differences represent special-cause variation and should be expressed as unacceptable rates per million results (ppm). We observed 447 ppm unacceptables: 196 ppm in control samples and 251 ppm in patients’ samples. Results judged likely to alter patient care occurred at a rate of 41 ppm. To better understand the magnitude of these rates, we compared these results with reports of error rates in HIV testing and the airline industry. The measurements reported were made for the purpose of quality improvement, not judgment or discovery. The significance of these findings for laboratorians, manufacturers, and regulators is discussed.

Research paper thumbnail of Esterolytic method for determination of heparin in plasma

Clinical Chemistry, 1981

This assay for heparin is based on the heparin-accelerated rate of alpha-thrombin III. The rate o... more This assay for heparin is based on the heparin-accelerated rate of alpha-thrombin III. The rate or product formation from the residual active thrombin is inversely proportional to plasma heparin content. The assay can be performed manually, but our results were obtained with a discrete analyzer, the ABA-100. The assay is insensitive to concentrations of antithrombin III in plasma. Precision studies gave CVs of less than 10%. This assay was compared to the Dade Protopath heparin assay and a correlation coefficient of 0.90 was obtained (n = 62). The correlation between activated partial thromboplastin times and heparin concentrations (r = 0.67) was calculated frm results on 78 plasma specimens from 10 patients.

Research paper thumbnail of Panel discussion: how to monitor and minimize variation and mistakes

Research paper thumbnail of Effects of bilirubin on detection of hydrogen peroxide by use of peroxidase

Clinical Chemistry, 1978

Bilitubin interferes with the quantitation of hydrogen peroxide in reagent systems in which perox... more Bilitubin interferes with the quantitation of hydrogen peroxide in reagent systems in which peroxidase is used. Difference spectra suggest that this interference is a combination of chemical and spectral effects. The data presented are most consistent with the following interpretation: (a) bilirubin destroys part of the reactive intermediate formed in the peroxidase reaction and thus decreases the amount of chromophore formed and (b) the spectra for bilirubin and the chromaphore overlap, which also affects the results. The relevance of these results to reagent design and laboratory quality control are discussed.

Research paper thumbnail of Enzymic inhibition assay for methotrexate with a discrete analyzer, the ABA-100

Clinical Chemistry, 1980

We adapted an inhibition assay for methotrexate, involving dihydrofolate reductase from bovine li... more We adapted an inhibition assay for methotrexate, involving dihydrofolate reductase from bovine liver, for use with a discrete analyzer (the ABA-100). The analyzer was used both for dilution and a 5-min pre-incubation of the sample with NADPH--enzyme reagent, and for the assay itself. The standard curve was linear between 10 and 120 microgram/L. Without pre-incubation the standard curve was nonlinear. The presence of albumin in the NADPH--enzyme reagent enhanced both enzyme activity and stability. Within-run precision (CV) was 2.0% (n = 24), run-to-run precision 7.1% (n = 49). Results obtained on patients' samples (29 sera, 15 urines, 18 cerebrospinal fluids) by the present method and a radioimmunoassay method did not differ statistically (p greater than 0.05) when the paired data were analyzed by use of the sign test and Wilcoxon's ranked sign test.

Research paper thumbnail of Serum uric acid determined by reversed-phase liquid chromatography with spectrophotometric detection

Clinical Chemistry, 1978

We describe a method for determining uric acid in serum by reversed-phase liquid chromatography w... more We describe a method for determining uric acid in serum by reversed-phase liquid chromatography with spectrophotometric detection at 280 nm. Serum, 100 ul is mixed with 100 u1 of a solution containing, per liter, 70 ml of acetonitrile in sodium acetate (20 mmol/Iiter, pH 4.0) and 500 mg of the internal standard, adenine. The mixture is allowed to stand in an ice bath for 3 mm, then centrifuged. A 7.5tl portion of the supernate is chromatographed on a “ Bondpak C18” column, with a 35 mI/liter solution of acetonitrile in sodium acetate (10 mmol/liter, pH 4.0) as the mobile phase. For 10 runs of duplicates, the within-run CV was 1.2% and the day-to-day CV (10 days) was 2.5% for a uric acid concentration of 53 mg/liter. Sera from 100 patients were analyzed for uric acid by the proposed method, a continuous-flow (SMA 12/60) method, and a uricase method; mean values for the 100 sera were 64, 71, and 64 mg/liter, respectively. Correlations were as follows: r = 0.987 for proposed method vs. SMA 12/60 and r = 0.997 for proposed method vs. the uricase method. The proposed method is sensitive and specific and we think it will be useful for evaluating other i.ilc acid methods for interference and specificity.

Research paper thumbnail of Presence of creatine kinase BB isoenzyme in some patients with prostatic carcinoma

Clinical Chemistry, 1977

We have observed creatine kinase isoenzyme BB in the sera of nine of 19 patients with Stage D car... more We have observed creatine kinase isoenzyme BB in the sera of nine of 19 patients with Stage D carcinoma of the prostate. Its presence does not seem to correlate with acid phosphatase activity in serum or the presence of bone metastases as indicated by increased alkaline phosphatase activity in serum. Only three of the nine patients with BB isoenzyme activity detectable in their serum had abnormal values for total creatine kinase activity, but all had abnormal values for alkaline and acid phosphatase activity. All 10 patients with no BB isoenzyme detectable had abnormal acid phosphatase values; however, only seven had increased alkaline phosphatase values and only one had increased creatine kinase activity.

Research paper thumbnail of Kinetic determination of serum lipase activity with the Abbott ABA-100

Clinical Chemistry, 1976

A turbidimetric procedure for lipase has been adapted for use on the Abbott Bichromatic Analyzer ... more A turbidimetric procedure for lipase has been adapted for use on the Abbott Bichromatic Analyzer (ABA-100). The method is rapid and results compared well with those by the more traditional method of Cherry and Crandall [Am. J. Physiol. 100, 266 (1932)]. Advantages of this method include shorter incubation time (2 min), smaller sample size (50 mul), neglible interference from bilirubin, and greater dynamic range (to eightfold normal).

Research paper thumbnail of Medically relevant laboratory-performance goals: a listing of the complexities and a call for action

Clinical Chemistry, 1993

This 1992 Clinical Chemistry Forum asks if accuracy and precision goals for the laboratory can be... more This 1992 Clinical Chemistry Forum asks if accuracy and precision goals for the laboratory can be specified by reference to medical requirements, which are a function of the total laboratory testing process as well as the needs of patients, clinicians, and societal institutions. Furthermore, medical decisions and decisions about medical requirements must be made in situations of uncertainty and thus are subject to predictable cognitive errors. The interaction of all these factors must be considered by patients, laboratorians, and clinicians to identify practical and effective performance goals. Pathologists and clinical chemists are uniquely trained to identify thoughtful clinicians who are knowledgeable in quantitative judgment to participate in this goal-setting endeavor. It is time for these parties to accumulate the available data and engage in the synthesis of effective performance goals.

Research paper thumbnail of Wellness Testing: Design and Experience of an Established Program

Clinics in Laboratory Medicine, 1993

Research paper thumbnail of Prediction of Bone Marrow Iron Findings from Tests Performed on Peripheral Blood

American Journal of Clinical Pathology, 1986

After evaluating multiple tests, the authors have devised a scheme to predict bone marrow iron fi... more After evaluating multiple tests, the authors have devised a scheme to predict bone marrow iron findings from tests performed on peripheral blood. They examined bone marrows from 97 consecutive patients with anemia who were divided into five marrow morphologic groups: (1) iron deficiency; (2) anemia of chronic disease; (3) abnormal sideroblasts; (4) ring sideroblasts; and (5) other. Tests of peripheral blood included hemoglobin, hematocrit, red blood cell count and red blood cell indices, reticulocyte count, sedimentation rate or zetacrit, ferritin, iron, iron binding capacity, free erythrocyte protoporphyrin, and tests of hepatic and renal function. Cluster analysis, multidimensional scaling, and logistic discriminant analysis were used to derive a graph of serum ferritin with the sedimentation rate, allowing accurate confirmation or exclusion of iron deficiency in most patients. Percent saturation of serum transferrin and serum ferritin allowed identification of only 50 percent of patients with abnormal or ring sideroblasts while excluding 100 percent of patients without abnormal or ring sideroblasts. In three years of follow-up, two of 19 patients with abnormal or ring sideroblast have developed the dysmyelopoietic syndrome or ANLL, respectively. With the aid of the two parameter graphs described, the authors believe the differential diagnosis of the hypoproliferative anemias relating to iron metabolism can frequently be made without examination of the bone marrow.