Laboratory tests are an important component of comprehensive medical evaluations. These tests provide helpful information that can complement or confirm clinical suspicion, and they can sometimes identify problems that are not clinically evident. On the other hand, tests may provide inaccurate or misleading information under certain circumstances.
Hyperphosphatemia is a relatively uncommon laboratory abnormality most often seen in patients with advanced renal failure, hypoparathyroidism, cellular lysis, or excessive phosphate intake (or iatrogenic administration). Hyperphosphatemia may occur artifactually from a hemolysed, icteric, or lipemic sample; a prolonged delay between blood draw and analysis; or heparin contamination. Hyperglobulinemia (paraproteinemia) has long been recognized to cause spurious serum phosphate readings because of analytical interference. Paraproteinemia is also known to affect many other laboratory parameters, including blood urea nitrogen, creatinine, bilirubin, calcium, iron, sodium, and lipoproteins.
The precise frequency with which these artifactual abnormalities are encountered in the clinic or laboratory is unknown, but the phenomenon is potentially substantially underrecognized. The frequency is likely to increase in the future. The prevalence of paraproteinemia increases with age, reaching >10% in persons >80 years of age. Older persons are also more likely to have multiple comorbidities and therefore require multiple laboratory tests. Thus, with the increasing mean age of the population, there are increasing opportunities for clinicians to encounter paraproteinemia-related artifactual laboratory abnormalities. The importance of recognizing this phenomenon is self-evident: to avoid misinterpretation of data and unnecessary testing. This possibility should be considered when encountering a totally unexpected abnormality that does not “fit” in the clinical context. When paraproteinemia is suspected, further evaluation should be undertaken in consultation with a laboratory medicine specialist. Repeating the test after deproteination, further dilution of the sample, or use of an alternative testing methodology are some of the strategies available for further investigation.
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Authors’ Disclosures of Potential Conflicts of Interest: No authors declared any potential conflicts of interest.
Role of Sponsor: The funding organizations played no role in the design of study, choice of enrolled patients, review and interpretation of data, or preparation or approval of manuscript.
- © 2010 The American Association for Clinical Chemistry