Quantitating low body fluid protein.

Q When our laboratory receives requests for fluid total protein, if the value is less than our lower linearity, we report <2.0 g/dL. We had only one complaint when a physician needed to quantitate values less than 2.0 g/dL, so we sent the specimen to a reference laboratory that could measure

A Measurement of total protein in body fluids other than blood, urine, or cerebrospinal fluid is usually done to differentiate an inflammatory fluid collection, an exudate, from one that is not inflammatory, a transudate. In synovial fluid from a joint, the normal protein concentration is 1 g/L to 3 g/dL. A value greater than this suggests an inflammatory effusion. Likewise, in pleural, peritoneal, and pleural fluids, 3 g/dL is usually taken as the cut-off value for differentiating transudates from exudates. Some authors use a lower cut-off of 2.5 g/dL.

Some references suggest using a ratio of fluid to serum protein to differentiate transudate from exudate. Perhaps the physician wants the protein value to use in such a formula, but the total protein value would also be high. Protein is just one of several markers that can be used for differentiating transudates from exudates.

Low total protein values are seen in patients with cirrhosis of the liver when ascites develops late in the disease. Patients with a low value, below 1.5 g/dL, are at greater risk of developing spontaneous bacterial peritonitis. Knowing that the concentration is low has some prognostic value, although it should not be a reason for beginning prophylactic antibiotic therapy. (1)

Reference

1. Arnaout WS, Demetriou AA. Hepatic Failure. In: Wilmore DW, et al, eds. ACS surgery: principles and practice. New York: WebMD Professional Publishing. 2004.

--Daniel M. Baer, MD

Professor Emeritus

Department of Pathology

Oregon Health and Science University

Portland, OR

Daniel M. Baer, MD, is professor emeritus of laboratory medicine at Oregon Health and Science University in Portland, OR, and a member of MLO's editorial advisory board.

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