RBCs in body fluids.

Q There was an article in the "Tips from the experts" regarding cell counts on body fluids. (October 2002, Quantitative body fluid counts, p. 39; November 2002, Differential with a normal CSF count, p. 39). I realize that you must perform both a WBC and RBC count on CSF. Are there any fluids

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A RBC counts are useful in peritoneal fluid, pleural fluid, pericardial fluid, synovial fluid, and cerebrospinal fluid. First, no RBCs should be present in body fluid under normal conditions. If numerous RBCs are present (except traumatic tap), it suggests a pathologic process. Malignancy, trauma, infarct, and hemorrhage are the major causes for bloody fluid. Second, correlating RBC with WBC counts is helpful to determine if increased WBCs are due to peripheral blood contamination.

The value of RBC counts in fluids, however, is somewhat limited. No RBC reference value is available for determining hemorrhage in any fluid. A small number of RBC (5,000/[micro]L to 10,000/[micro]L) will produce a blood-tinged fluid that may be found in transudates, exudates, and a small amount of bleeding. Higher RBC counts (>100,000/[micro]L) in pleural fluid are highly suggestive of malignancy, trauma, or pulmonary embolus/infarct. RBC counts are also used in peritoneal lavage fluids for assessing blunt and penetrating trauma, as well as other conditions.

Accurate RBC count has a limited differential diagnostic value in body fluids; however, it should not be entirely ignored either.

--Eric Nutt, MT (ASCP)

--Guang Fan, MD, PhD

Pathology Department

Oregon Health & Science University

Portland, OR