Approach to the analysis of body fluids for the detection of infection

Sterile body fluids represent an important source for the diagnosis of infectious diseases because they can be sampled by sterile methods that bypass the normal bacterial flora so heavily colonizing the body surface. Thus when these specimens are received, full advantage should be taken to perform complete microscopic and cultural tests for viral, bacterial, mycobacterial, fungal, and parasitic diseases. In many cases the evaluation can be tailored to the types of organisms that are likely to infect particular body cavities. Ideally, the workup could also be based on the history, clinical presentation, and preliminary examination of the patient, but under most circumstances it may be more appropriate for the laboratory to proceed with a more complete workup of these vital specimens than physicians request. Specimens should be transported promptly to the laboratory and should be viewed quickly by Gram's or acridine orange stain and, in selected situations, also by acid-fast stain, direct fluorescence for legionellosis, and direct wet mount for parasites. Results of these studies should be called in without delay to the responsible physician. Cultures should also be inoculated as soon as possible. Nonspecific tests, including the cell count and protein, glucose, lactic acid, and LDH levels, may provide valuable clues to the presence of infection. Direct antigen detection does not replace traditional microscopic and cultural evaluation of these specimens but may have supplemental value.