Procalcitonin-Based Guidelines and Lower Respiratory Tract Infections

Abstract

To the Editor: In a randomized controlled trial, Dr Schuetz and colleagues studied the effect of a procalcitonin (PCT) algorithm in the antibiotic management of lower respiratory tract infections (LRTIs) in emergency departments of tertiary hospitals. Procalcitonin showed promise in helping to limit antibiotic therapy to those patients who are likely to benefit in inpatient settings where follow-up measurements are accessible and waiting time to obtain blood test results is short. In their discussion, the authors called for more widespread introduction of PCT measurement for milder LRTIs in outpatient physician offices. We think this conclusion is not justified because their study patients were managed in tertiary care settings. By focusing on the sickest patients with LRTI, the PCT test may have had better sensitivity in the study patients than it would have in less ill patients observed in primary care, a form of spectrum bias. Procalcitonin did not perform well in a prior study based in primary care. Despite a recent study showing efficacy and safety of a PCT approach to the restriction of activities of patients with LRTI in primary care, pragmatic evidence that the use of PCT for LRTI management in primary care leads to a reduction in antibiotic use is lacking. Explanatory trials evaluate efficacy in controlled conditions, and pragmatic trials evaluate effectiveness in usual care. How useful a trial is depends not only on the design but also on the similarity between the trial and the clinician’s context. It seems doubtful that introducing a costly test, not readily available as a near-patient test at present, will change physicians’ decision making. Moreover, such use runs a risk of defining a test result as a medical problem. In contrast, other less costly biomarkers, including C-reactive protein (CRP), have shown test characteristics similar to PCT when assessed in an outpatient population, and there is pragmatic evidence of the effectiveness of CRP testing when used at the point of care in a primary care setting. Before widespread use of PCT in primary care can be advocated, pragmatic evidence of the comparative and cost-effectiveness of different point-of-care strategies is needed.