Lithium heparin samples generated minimal numbers and percentages of points violating the error tolerance criteria (Table 2). Ethylenediaminetetraacetic acid tended to decrease glucose meter results obtained with most of the systems.
The negative bias of the Precision PCx system for samples containing EDTA resulted in a high frequency of values falling outside the lower error tolerance. Note that vendor specifications for the One Touch II state that using EDTA may cause inaccurately low results if the sample hematocrit exceeds 55%.
For uniformity of comparison and interpretation of results, the effects of both heparin and EDTA were evaluated on all four systems, even though test strip package inserts may not rule out the use of EDTA explicitly. However, lithium heparin was recommended as an acceptable anticoagulant in the package inserts of all four glucose meter systems.
The results of this study show that minimal analytical errors were produced when lithium heparin was used as the sample anticoagulant. A recent study showed that sodium citrate, used to anticoagulate indwelling arterial catheters, interferes with reliable measurements of glucose and other analytes, even after discarding 9 mL of blood.33 Hence, samples taken from such lines may produce errors. With whatever additive is used, or without any additive, whole-blood and plasma specimens should be processed promptly to avoid preanalytical changes due to the metabolism of glucose.34
The authors recommend that users of glucose meter systems: a) consult the package insert for anticoagulant specifications, b) contact the manufacturer for current information, and if necessary, c) perform an appropriate investigation when unusual additives (e.g., thrombin inhibitors35,36) are necessary. The type of anticoagulant in the collection device, if used, should be clarified. To reduce the potential for medical errors in point-of-care glucose testing,37 the relative effects of different specimen anticoagulants should be considered and communicated carefully when conducting comparison studies, planning clinical applications, and interpreting glucose results.
The authors thank the companies who contribute generously to the POCT·CTR and enabled this research to be performed. This research was presented by Richard Louie, recipient of a Young Investigator Award, at the annual meeting of the Academy of Clinical Laboratory Physicians and Scientists in Seattle in June, and by Judith Lee at the annual meeting of the American Association for Clinical Chemistry in Chicago in July, 2001.
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