pH, Body Fluid

Laboratory assay overview

This test is used to determine pH of body fluid.

Laboratory assay overview

This test is intended to assess pH in body fluids. pH can indicate whether a fluid is acidic, alkaline, or neutral. The pH of the blood is approximately 7.4 [1]. The clinical significance of the pH of pleural, pericardial, gastric, and ocular fluids has been described. The clinical significance of pH alterations of many other body fluids is not known. pH of pleural fluid may be ordered when evaluating the nature of a pleural effusion. A transudative pleural effusion due to pressure-induced fluid leakage typically has a pH in the range of 7.45 to 7.55, whereas an exudative pleural effusion due to inflammation-mediated fluid leakage generally has a pH in the range of 7.30 to 7.45 [2]. The American College of Chest Physicians defines a complicated parapneumatic (or pleural) effusion as one that has a pH less than 7.2 and suggests aggressive management of such effusions [3,4]. The pH of pericardial fluid has been used to differentiate between inflammatory (pH 7.06 +/- 0.07) and non-inflammatory (pH 7.42 +/- 0.06) causes of pericardial effusions [5]. The pH of gastric contents has been defined as less than 3.5. Any value above that is considered abnormal [6]. The pH of ocular fluid has been defined as approximately 7.0 [7]. Measurement of ocular fluid pH may be used following chemical injury to the eye to assess adequacy of flushing in the removal of the chemical agent. pH of ascitic (peritoneal) fluid has been shown to correlate with neutrophil count but is generally considered nonspecific in the evaluation of cause for fluid accumulation within the abdomen [8]. pH measurements of body fluid are most informative when used as adjunctive data, alongside additional clinical, laboratory, and radiographic findings, as well as to support a pretest clinical assessment [2]. This test is performed using a pH meter [2-4]. This test should be interpreted in the context of pertinent clinical history and physical examination findings. References 1. Burtis C, et al. Tietz Fundamentals of Clinical Chemistry and Molecular Diagnostics. St Louis, Missouri: Elsevier; 2015:310-314. 2. Sahn SA. Am J Med Sci. 2008;335:7-15. 3. Colice GL, et al. Chest. 2000;118:1158–1171. 4. Putnam B, et al. Curr Opin Pulm Med. 2013;19:357-361. 5. Kindig JR, et al. Am J Med. 1983;75:1077-1079. 6. Lu P-J, et al. World J Gastroenterol. 2010;16:5496-5501. 7. Coles WH, et al. Br J Ophthalmol.1984;68:549-552. 8. Runyon BA, et al. Hepatology. 1991;13:929-935.