Does serum procalcitonin have a diagnostic value in febrile adult patients presenting to the emergency department?

Hausfater and colleagues stated that in febrile adult patients presenting to the emergency department (ED) a procalcitonin (PCT) ≥0.2 mcg/l can help physicians to identify bacterial/parasitic infections [1]. We disagree and want to illustrate that by calculating likelihood ratios (LR). A LR is a semi-quantitative measure of the performance of a diagnostic test, expressing the magnitude by which the pre-test probability of a diagnosis in a given patient is modified by the results of a test [2]. A positive result with a high positive likelihood ratio (LR+) can rule in a diagnosis. A negative result with a low negative likelihood ratio (LR-) can rule out a diagnosis. LR+ for the emergency physician 1.98, LR0.26. Using prevalence of bacterial/parasitic infections as pre-test probability, a positive diagnosis by the physician modified pre-test probability from 69% to 82% and a negative diagnosis to 37%. PCT ≥0.2 mcg/l, LR+ 1.88 and LR0.39. Pre-test probability changed to 81% by PCT ≥0.2 mcg/l and to 47% by PCT < 0.2 mcg/l. The performance of the emergency physician is based on anamnesis, physical examination and traditional markers such as neutrophil leukocytes and C-reactive protein (CRP). For example, CRP ≥40 mg/l, LR+ 2.0, LR0.39. Pre-test probability changed by CRP ≥40 mg/l to 82% and to 47% by CRP < 40. Will the likelihood ratios of the emergency physician change much when PCT is added to the spectrum of available diagnostic tests? We don’t think so.