Discriminating Disease Flare From Infection in Febrile Patients With Systemic Lupus Erythematosus in a Safety-Net Hospital System: A Multicenter Study - PubMed (original) (raw)

Discriminating Disease Flare From Infection in Febrile Patients With Systemic Lupus Erythematosus in a Safety-Net Hospital System: A Multicenter Study

Abhimanyu Amarnani et al. ACR Open Rheumatol. 2025 Jun.

Abstract

Objective: The objective of this study was to assess clinical laboratory parameters that distinguish between disease flare and infection in febrile patients with systemic lupus erythematosus (SLE) at safety-net hospitals in Los Angeles.

Methods: We reviewed electronic medical records of patients admitted from August 1, 2016, through July 31, 2019, categorizing them as disease flare, bacterial infection (culture positive), culture-negative infection, and both flare and infection. Laboratory parameters collected within 48 hours of admission (complete blood cell count with differential, liver function panel, erythrocyte sedimentation rate [ESR], C-reactive protein [CRP], C3, C4, lactate, procalcitonin, and ferritin) were analyzed.

Results: Several laboratory parameters significantly distinguished febrile patients with disease flare from those with infection. An optimized multivariable logistic regression model revealed that an elevated ESR:CRP ratio (>1.17), low white blood cell (WBC) count (<6.25 × 109/L), low absolute neutrophil count (<5.55 × 109/L), and low CRP (<113 mg/L), C3 (<44.5 mg/dL), and C4 (<13.5 mg/dL) levels helped discriminate disease flare from culture-positive infection. These laboratory parameters yielded areas under the receiving operating characteristic curve of 0.87 (95% confidence interval [CI] 0.76-0.97) for flare versus culture-positive infection and 0.94 (95% CI 0.88-1.00) for flare versus culture-negative infection. These optimized models, using multiple laboratory parameters, significantly outperformed the ESR:CRP ratio alone (P < 0.02) in discriminating flare from infection.

Conclusion: The ESR:CRP ratio plus C3 and C4 levels, WBC count, neutrophil count, and monocyte count discriminate flare from either culture-positive or culture-negative infection in febrile patients with SLE. Our findings warrant prospective validation.

© 2025 The Author(s). ACR Open Rheumatology published by Wiley Periodicals LLC on behalf of American College of Rheumatology.

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Figures

Figure 1

Figure 1

Distribution of laboratory parameters across groups. Scatter plots for (A) ESR:CRP ratio, (B) ESR, (C) CRP, and (D) age. Data are presented as individual points and mean ± 95% confidence interval. *P < 0.05, **P < 0.01, and ***P < 0.001; nonparametric one‐way analysis of variance tests (Kruskal–Wallis) with Dunn's post hoc pairwise multiple comparisons. CRP, C‐reactive protein; CultPosInfec, culture‐positive infection; CultNegInfec, culture‐negative infection; ESR, erythrocyte sedimentation rate.

Figure 2

Figure 2

Distribution of leukocyte laboratory parameters (A) White blood cell count, (B) neutrophil count, (C) monocyte count, and (D) lymphocyte count. Data are presented as individual points and mean ± 95% confidence interval. *P < 0.05, **P < 0.01, and ***P < 0.001; nonparametric one‐way analysis of variance tests (Kruskal–Wallis) with Dunn's post hoc pairwise multiple comparisons. CultPosInfec, culture‐positive infection; CultNegInfec, culture‐negative infection.

Figure 3

Figure 3

Disease flare versus infection discrimination by logistic regression modeling of the ESR:CRP ratio alone versus with optimized laboratory parameters. (Left) ROC curves of disease flare versus positive culture infection comparing the ESR:CRP ratio alone (red) versus the optimized model of age + WBC count + ANC + C4 level + CRP level + ESR:CRP ratio (blue). (Right) ROC curves of lupus fare versus negative culture infection comparing the ESR:CRP ratio alone (red) versus the optimized model of age + ESR:CRP ratio + AMC + C4 level + C3 level + ANC (blue). P values represent multivariate logistic regression between models. AMC, absolute monocyte count; ANC, absolute neutrophil count; AUC, area under the curve; CRP, C‐reactive protein; ESR, erythrocyte sedimentation rate; ROC, receiver operating characteristic; WBC, white blood cell.

Figure 4

Figure 4

Disease flare versus infection discrimination by logistic regression modeling of the ESR:CRP ratio alone versus with standardized laboratory parameters. (Left) ROC curves of disease flare versus positive culture infection comparing the ESR:CRP ratio alone (red) versus the standardized model of age + WBC count + ANC + C4 level + ESR:CRP ratio (blue). (Right) ROC curves of lupus flare versus negative culture infection comparing the ESR:CRP ratio alone (red) versus the standardized model of age + WBC count + ANC + C4 level + ESR:CRP ratio (blue). P values represent multivariate logistic regression between models. ANC, absolute neutrophil count; AUC, area under the curve; CRP, C‐reactive protein; ESR, erythrocyte sedimentation rate; ROC, receiver operating characteristic; WBC, white blood cell.

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