The prevalence of sepsis in an intensive care unit is high compared with that in the emergency department, and the positive predictive values and accuracy of procalcitonin for sepsis might markedly differ between these two settings. This issue is of paramount importance because disease prevalence can markedly differ from one population to another. Figure 2shows the influence of prevalence on the various diagnostic indices. 17Īlthough sensitivity and specificity are not markedly influenced by the prevalence of the disease, negative predictive value, positive predictive value, and accuracy are affected by prevalence. 16However, intervention studies are lacking for many novel biomarkers or give conflicting results for others. For example, several studies nicely demonstrated that a diagnostic strategy based on procalcitonin level reduces antibiotic use for acute respiratory tract infections, exacerbation of chronic obstructive pulmonary disease, and ventilator-associated pneumonia. 15Assessment of the usefulness mainly involves both characteristics of the test itself such as cost, invasiveness, technical difficulties, rapidity, and characteristics of the clinical context (prevalence of the disease, consequences of outcome, cost, and consequences of therapeutic options).ĭemonstrate that the measurement of the biomarkers modifies outcome (intervention studies). 7Īssess the usefulness of the biomarker, which should be clearly distinguished to the quality of diagnostic information provided. For example, although the accuracy of procalcitonin to diagnose postoperative infection after cardiac surgery was lower than that of physicians, procalcitonin enabled to make the diagnosis earlier. For example, in the diagnostic setting, although unknown, the outcome (the disease) has occurred, whereas in the prognostic setting, the outcome remains to be determined and can only be estimated as a probability or a risk, and the uncertain nature of this outcome should be considered.ĭemonstrate that the biomarker is significantly modified in diseased patients as compared to control.Īssess the diagnostic properties of the biomarkers.Ĭompare the diagnostic properties of the biomarker to existing tests.ĭemonstrate that the diagnostic properties of the biomarker increase the ability of the physician to make a decision this might be difficult to analyze because timing of diagnosis may be crucial and not easy to identify. 14However, the purpose of diagnostic and prognostic settings markedly differ. For example, blood lactate levels have been proposed for risk stratification of sepsis. 8Biomarkers are often used for risk stratification. 6In contrast, it is considered only as a severity biomarker in pulmonary embolism, 9whereas procalcitonin is considered both as a diagnostic and severity biomarker of infection. For example, cardiac troponin I is a very sensitive and specific biomarker of myocardial infarction in the postoperative period in noncardiac surgery.
A biomarker may provide a diagnosis or assess severity (or assess a risk). A biomarker may serve different roles ( table 1) and, thus, need to accomplish several reporting goals.