Lithium heparin for specimen collection.

Lithium heparin for specimen collection

Q I work in a physician's office laboratory. We are trying to increase turnaround time, and I would like to use lithium heparin tubes instead of serum for pregnancy tests, as well as chemistry and special chemistry to include TSH, fT4, T3, and PSA. My senior techs say that only serum may be used. What do you say?

A The appropriateness of whether a particular anticoagulant can be used for testing of a particular analyte is a common question directed towards many laboratories. Historically, serum has been the preferred assay material for determining concentrations of many blood constituents. Today, plasma is preferred for many, but not all, laboratory investigations. Plasma better reflects the physiologic matrix of the patient and yields 15% to 20% more volume compared with serum from the same volume of whole blood. (1) In addition, the time for processing plasma is shorter compared with serum, helping laboratories decrease the time needed for the testing process; however, use of plasma vs. serum for testing can introduce some problems. Contamination of the sample with cations such as NH4+, Li+, Na+, or K+ can affect some assays, and heparin itself can inhibit some reactions.

There is no easy answer to your question due to a number of factors. The optimal speciman type for a particular analyte may differ according to assay vendor or type of assay method that is used. In addition, the stability of some analytes varies, depending upon whether it is present in serum or plasma. Reference ranges for a particular analyte may have been established using a specific sample type; therefore, switching to an alternate sample type will require reverification of reference ranges. A very good summary can be found in reference one below; however, each laboratory should establish guidelines that are appropriate for its own particular assay methods.

Many studies have evaluated the effects of different sample types on blood constituents. Evaluations of some routine biochemical analytes such as chloride, magnesium, calcium, cholesterol, triglycerides, glucose, creatinine, albumin, lactate dehydrogenase using serum, and heparinized plasma revealed no significant differences in the values obtained for these particular analytes. (2), (3) Heparin is said to inhibit acid phosphatase activity (4) and to affect the binding of triiodothyronine and thyroxine to their carrier proteins, thus producing falsely higher concentrations of these hormones. (4)

--Veselina Korcheva, MD

Department of Pathology

Oregon Health and Science University

Portland, OR

References

(1.) Banfi G, Bauer K, Brand W, Buchberger M, Deom A, Ehret W, et al. Use of Anticoagulants in Diagnostic Laboratory Investigations. Geneva, Switzerland: World Health Organization; 2002. WHO document WHO/DIL/LAB/99.1 Rev 1.

(2.) Boyanton BL Jr, Blick KE. Stability studies in twentyfour analytes in human serum or plasma. Clin Chem. 2002;48(12):2242-2247.

(3.) Boeynaems JM, De Leener A, Dessars B, et al. Evaluation of a new generation of plastic evacuated bloodcollection tubes in clinical chemistry, therapeutic drug monitoring, hormone and trace metal analysis. Clin Chem Lab Med. 2004;42(1):67-714.

(4.) Burtis C, Ashwood E, Bruns D. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 4th ed. St. Louis, MO: Saunders Elsevier; 2006.

Edited by Daniel M. Baer, MD