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Stabilizing whole blood for glucose-comparison testing.

Q We have over 100 glucose meters in our hospital for which we perform monthly comparison testing. We use a heparinized whole-blood sample, which also is assayed on our main lab instrument. It is a continual frustration because the glucose, of course, drops in value over the two- to three-hour period of time that we test the meters. We realize that we are going above and beyond what is required for these comparisons, but it is a process that we intend to continue. Do you know of any way to stabilize the glucose sample? Heparin is the only acceptable anticoagulant for the LifeScan strips we use.

A Stabilized whole-blood products are available from commercial sources for QC, proficiency testing, and calibration verification of glucose meters; but for a large institution with many meters, this is expensive.

Glucose concentrations decrease rapidly in unpreserved anticoagulated whole blood at room temperature. The glucose loss is linear, declining about 10 mg/dL per hour. (1) Sodium fluoride commonly has been used to stabilize the glucose, but it is not effective as an antiglycolytic agent for an hour or more after blood collection, with a mean glucose loss of about 5% in the first four hours. (1,2) Iodoacetate. another preservative, has a similar lag time before it is an effective glycolytic agent. After the initial glycolysis, glucose preserved with fluoride is stable for several days at ambient temperature, and the samples can be used for comparison testing in those systems for which fluoride tubes are acceptable.

For some meters that use a glucose-dehydrogenase reaction, blood preserved with sodium fluoride is an acceptable sample and can be used for comparison testing of meters. In other meters, however, such as LifeScan's SureStepPro, that use a glucose oxidase reaction, sodium fluoride inhibits the reaction and cannot be used.

Glyceraldehyde has been proposed as an antiglycolytic preservative for whole blood. It is effective immediately and for at least eight hours. (3) I was unable to find data validating its use in glucose meters, but a patent has been issued for a stable whole-blood calibrator control for glucose instruments. (4) The patent descriptions contains instructions for preparing the material.

Another approach is to use plasma instead of whole blood. Once it is separated from cells, little glycolysis occurs in plasma. (1) This is the method recommended by LifeScan in its technical bulletin for calibration verification of SureStepPro meters. (5) The bulletin contains instructions for preparing spiked plasma samples that can be used for comparison testing.

--Daniel M. Baer, MD

Professor Emeritus

Department of Pathology

Oregon Health and Science University

Portland, OR

References

1. Chan AY, Swaminathan R, Cockram CS. Effectiveness of sodium fluoride as a preservative of glucose in blood. Clin Chem. 1989;35:315-317.

2. Waring WS, Evans LE, Kirkpatrick CT. Glycolysis inhibitors negatively bias blood glucose measurements: potential impact on the reported prevalence of diabetes mellitus. J Clin Pathol. 2007;60:820-923.

3. Landt M. Glyceraldehyde preserves glucose concentrations in whole blood specimens. Clin Chem. 2000;46:1144-1149.

4. Ryan WL, Hunsley BA, inventors. Process, composition, and kit for providing a stable whole blood calibrator/control [abstract]. US patent 20,060,188,995. http://www.freepatentsonline.com/20060188995.html. Accessed August 19, 2007.

5. SureStepPro Professional Blood Glucose Management System calibration verification. LifeScan technical bulletin 054-869A. http://www.lifescan.com/pdf/hospital/tb869.pdf. Accessed August 19, 2007.
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Title Annotation:Answering your questions
Author:Baer, Daniel M.
Publication:Medical Laboratory Observer
Geographic Code:1USA
Date:Feb 1, 2008
Words:561
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