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Clearing lipemic serum.

Q Is it acceptable to clear lipemic serum in a high-speed centrifuge (13,000 rpm for 30 minutes seems to work well) in order to produce more accurate chemistry results? Some labs use ultracentrifuges for this purpose, but they require a large amount of serum and are not always reliable (the specimen is often lost). My manager will not make this a standard practice until I can cite a reference stating this is acceptable. Instrument references indicate lipemia interferences can be eliminated by clearing the serum, though they do not indicate how it is done.

A Along with hemolysis and icterus, lipemia is one of the most commonly encountered conditions that cause interference in clinical laboratory testing. (1,2) Lipemia has been shown to affect the measurement of a wide range of analytes. (3,4) Displacement of water in a sample may lead to pseudohyponatremia when electrolytes are measured by indirect methods. (5) Unlike hemolysis or icterus, the interference caused by lipemia can be reduced by removal of the interfering lipid. Several methods have been proposed, such as ultracentrifugation, filtration, and solvent extraction. (6) My only problem with your method is that excess heat may occur in an unrefrigerated centrifuge, which could affect the integrity of the cellular components and cause the release of potassium. A refrigerated sample and/or centrifuge would make the separation of chylomicrons from the sample easier but would not reduce the VLDL fraction. Reference 6 states this is acceptable.

References

1. Ryder KW, Trandle DS, Bode MA, Cole RE, Moorehead WR, Glick MR. Effects of hemolysis, icterus, and lipemia and automated immunoassays. Clin Chem. 1993;37(6):1134-1135.

2. Ryder KW, Glick MR. Erroneous laboratory results from hemolyzed, icteric, and lipemic specimens. Clin Chem. 1993;39(1):175-176.

3. Brady J. O'Leary N. Interference due to lipaemia in routine photometric analysis--survey of an underrated problem. Ann Clin Biochem. 1994;31:281-288.

4. Bossuyt X, Blanckaert N. Evaluation of interferences in rate and fixed-time nephelometric assays of specific serum proteins. Clin Chem. 1999; 45(1):62-67.

5. Weisberg LS. Pseudohyponatremia: a reappraisal. Am J Med. 1989;86:315-318.

6. Baer DM. Chemical Tests in Hyperlipidemic Samples. American Society of Clinical Pathologists. Check Sample: Clinical Chemistry No. CC-86, 1974.

--Ronald D. Feld, PhD, DABCC

Director, Clinical Chemistry

University of Iowa Hospitals and Clinics

Iowa City, IA
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Title Annotation:Answering your questions
Author:Feld, Ronald D.
Publication:Medical Laboratory Observer
Date:Nov 1, 2004
Words:389
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