LabNotes - Volume 13, No.3, Summer 2003

Did You Know...

CAP (College of American Pathologists) revised the Checklist* section for Hematology and Coagulation in November 2002. There are several revisions to this section including a new question recommending the use of 3.2% buffered sodium citrate instead of the 3.8% citrate concentration. The commentary discusses the reasoning behind the recommendation. If a laboratory currently uses 3.8% sodium citrate tubes they must provide data indicating that this concentration produces accurate and precise coagulation results. To meet your laboratory compliance needs, BD offers an array of BD Vacutainer® Plus Plastic Citrate Tubes including the 3.2% sodium citrate concentration.

CAP Checklist
Hematology and Coagulation - Nov 2002

Question: HEM.22748 Phase I

Are all coagulation specimens collected into 3.2% buffered sodium citrate?

Note: The milder chelation of 3.2% citrate over 3.8% citrate is preferred for accuracy of results.

Sodium citrate is effective as an anticoagulant due to its mild calcium-chelating properties. Of the two commercially available forms of citrate, 3.2% buffered sodium citrate (109 mmol/L of the dihydrate form of trisodium citrate Na₃C₆H₅O₇ 2H₂0) is the recommended anticoagulant for coagulation testing. The citrate concentration in 3.8% sodium citrate is higher and its use may result in falsely lengthened clotting times with calcium-dependent coagulation tests (i.e., PT and aPTT) with slightly underfilled samples and with samples with high hematocrits. Coagulation testing cannot be performed in samples collected in EDTA due to the more potent calcium chelation. Heparinized tubes are not appropriate due to the inhibitory effect of heparin on multiple coagulation proteins.

If the laboratory does not adhere to recommendations for use of 3.2% buffered sodium citrate, it must have data on file to demonstrate that the alternative citrate concentration produces accurate and precise coagulation results.

References:

1. Adcock DM, et al. Effect of 3.2% vs 3.8% sodium citrate concentration on routine coagulation testing. Am J Clin Pathol. 1997;107:105-110.
2. Reneke, J et al. Prolonged prothrombin time and activated partial thromboplastin time due to underfilled specimen tubes with 109 mmol/L (3.2%) citrate anticoagulant. Am J Clin Pathol. 1998;109:754-757.
3. NCCLS. Collection, transport and processing of blood specimens for coagulation testing and general performance of coagulation assays - third edition; approved guideline H21-A3. Wayne, PA: NCCLS, 1998.

*CAP laboratory accreditation guideline
For more information, visit www.cap.org.

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