Evaluation of Different Mixing Procedures for K2 EDTA Primary Samples on Hematological Testing

Giuseppe Lippi, MD; 1 Gian Luca Salvagno, MD; 1 Martina Montagnana, MD; 1 Giuseppe Banfi, MD; 2 Gian Cesare Guidi, MD1

Disclosures

Lab Med. 2007;38(12):723-725. 

In This Article

Abstract and Introduction

Background: Although it is recommended that primary tubes containing an additive should be mixed several times, there is no evidence that unmixed specimens will provide unreliable results in hematological testing.
Methods: Three primary 3.0-mL siliconized vacuum tubes containing 5.4 mg K2 ethylene diamine tetraacetic acid (EDTA) were sequentially collected from 20 healthy volunteers. The first was not inverted, was left standing in a vertical position, and then analyzed. The second and third tubes were respectively inverted 6 and 12 times immediately after collection and then analyzed.
Results: When compared with the reference specimens inverted 6 times, results on unmixed specimens revealed significant decreases for red blood cell count, hemoglobin, hematocrit and platelets count, whereas the mean platelet volume was significantly increased. In none of the specimens were results flagged for platelet clumping, nor did the differences exceed the acceptable limits of bias.
Conclusion: Provided the tubes are filled to their nominal volume, the blood-to-anticoagulant mixture occurring during sample collection may be adequate.

Results of hematological testing are integral to clinical decision making, provided that accurate and appropriate procedures are followed throughout the total testing process. Since the large majority of errors occur within the extra-analytical areas of testing, several preanalytical activities have a strong influence on results reliability, especially the most manually-intensive ones associated with the collection and handling of specimens.[1] Anticoagulants are commonly added to collection tubes to prevent clot formation in vitro and to maintain blood in the fluid state for hematological testing. Historically, ethylene diamine tetraacetic acid (EDTA) has been recommended as the anticoagulant of choice for hematological testing, since it allows the best preservation of cellular components and morphology of the blood cells.[2] Accordingly, blood collection tubes for hematological testing must be filled to the correct volume to ensure a proper blood-to-additive ratio, and adequately mixed to prevent clotting. Although the Clinical and Laboratory Standards Institute (CLSI) recommends that primary tubes that contains an additive should be gently mixed 5 to 10 times to allow a complete interaction between blood and anticoagulant,[3] there is no evidence that alternative mixing procedures for primary samples would influence the results of hematological testing. This lack of reliable information prompted us to determine the influence of primary tube mixing on hematological testing and, in particular, the minimal amount of inversions required for the primary specimens immediately after collection to enable clinically-reliable results in hematological testing.

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