Test performance of beta-glucan for Pneumocystis jirovecii pneumonia put in a clinical context
Pneumocystis jirovecii pneumonia (PCP) is often a difficult diagnosis to make in AIDS patients, as the best available test, namely immunofluorescence of respiratory samples, has a very high specificity but poor sensitivity . So, whereas positive results confirm the diagnosis, negative results are common and do not exclude it. The clinician must often start empiric therapy even when the pretest probability is relatively low, given the grave consequences of untreated PCP and the relatively low side effect profile of the treatment. A negative immunofluorescence test rarely has sufficient power to exclude the diagnosis and allow discontinuation of therapy, which in practice usually only happens when a clear alternative diagnosis is found. The priority for a new test therefore is high enough sensitivity to adequately exclude the diagnosis when negative, although high specificity would also be desirable.