Serum C-reactive protein (CRP) level and erythrocyte sedimentation rate (ESR) are the two most commonly used markers of inflammation in clinical practice. Reducing the need for these tests could lead to considerable cost savings without sacrificing the quality of patient care.
The electronic medical records of patients with systemic rheumatic diseases seen between May 2015 and June 2017 in the rheumatology clinics at a single academic medical center were retrospectively reviewed. Correlations and receiver operator characteristic (ROC) curves between serum CRP level and ESR vs serum globulin gap (the difference between levels of total protein and albumin) and albumin-to-globulin (A:G) ratio were determined.
In two independent cohorts (discovery: 263 subjects, 446 entries; validation: 438 subjects, 1959 entries), the globulin gap and A:G ratio correlated (p < 0.001) with CRP level and ESR, with correlation coefficients being greater for ESR than for CRP level. ROC curve analyses demonstrated better area-under-curve for ESR than for CRP level. The percentages of entries with elevated globulin gap (≥4.0 g/dl) and low A:G ratio (<0.8) were ∼8.4% and ∼2.6%, respectively, and each had a positive predictive value of ≥0.960 for elevated ESR. Among patients with high globulin gap, the change in globulin gap over time faithfully reflected changes in ESR.
In the subset of systemic rheumatic disease patients who harbor an elevated globulin gap, the ESR is almost always elevated. This novel observation sets the conceptual foundation and rationale for subsequent prospective studies that assess whether ESR testing in this subset of rheumatic disease patients could be reduced without sacrificing patient care. Ultimately, ordering an ESR test may often be unnecessary, thereby resulting in cost savings.