Pneumonia in the immunocompromised host: the role of bronchoscopy and newer diagnostic techniques.

The microbiology laboratory plays an essential role in the laboratory diagnosis of pneumonia in the immunocompromised host. Both the diversity of underlying or predisposing host conditions that increase risk for pneumonia and the variety of microbial agents that may be etiologically responsible make the laboratory's role in the diagnostic process a challenging one. In addition, the laboratory has a number of diagnostic tools available for detection of etiologic agents including conventional stains and cultures as well as newer tests relying on antigen detection and molecular techniques. Respiratory specimens available for testing are also diverse and are often obtained by the use of fiberoptic bronchoscopy, but may be complemented by use of blood samples when dissemination is likely or more recently by urinary antigen testing in select cases. Given the large number of variables in the design of a diagnostic approach to pneumonia in the immunocompromised host, it is critical that laboratorians and clinicians cooperate in the development of protocols that are cost effective and appropriate to their specific clinical settings.