Laboratory testing can be performed on many types of fluids from the body other than blood. Often, these fluids are tested instead of blood because they can give more direct answers to what may be going on in a particular part of the body.
Some body fluids that may be tested include:
Samples are usually obtained through collection of the fluid in a container (e.g., urine, semen) or by inserting a needle into the body cavity and aspirating with a syringe a portion of the fluid (e.g., CSF, pericardial fluid). For additional general information on how various samples are collected, see Collecting Samples for Testing.
Once a sample is obtained, a variety of tests may be performed, including chemistry tests, microscopic examinations, genetic tests, and infectious disease tests.
For certain body fluids, including pleural, pericardial, and peritoneal fluids, it is important to determine through testing whether the fluid is a transudate or an exudate because it can help diagnose the disease or condition present.
Block, D and Florkowski, C., Body Fluids. In: Rifai N, ed. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. St Louis, MO: Elsevier; 2018: Chap 43.