Coagulation Testing on an EDTA Specimen

Coagulation Testing on an EDTA Specimen
Jul 30, 2015 10:04am

Hi George: We encountered a case recently where we were asked to perform coagulation testing on specimens collected in EDTA vacutainers. The patient was refusing to give more blood than already collected for further coagulation tests and the attending doctor requested us to perform the tests in the blood collected in EDTA vials. We refused considering the protocols to be followed for coagulation testing, but was wondering as to what difference the same would have made in the values if the tests were actually performed.The tests requested were PT , PTT , fibrinogen and factor VIII .

Thanks, Dr Siddhartha Sharma


Hello, Dr. Sharma, and thank you for your question. You were absolutely correct, you cannot generate accurate coagulation results from an EDTA specimen, a problem that occasionally affects reference laboratories. In particular the PT and PTT results are markedly prolonged, and factor levels are markedly reduced. The issue is addressed in Adcock-Funk DM, Lippi G, Favaloro EJ. Quality standards for sample processing, transportation, and storage in hemostasis testing. Semin Thromb Hemost 2012;38: 576–85, and is reflected in the CLSI H21-A5 standard. I hope this helps.

2 Comments

Hi George: We encountered a case recently where we were asked to perform coagulation testing on specimens collected in EDTA vacutainers. The patient was refusing to give more blood than already collected for further coagulation tests and the attending doctor requested us to perform the tests in the blood collected in EDTA vials. We refused considering the protocols to be followed for coagulation testing, but was wondering as to what difference the same would have made in the values if the tests were actually performed.The tests requested were PT , PTT , fibrinogen and factor VIII .

Thanks, Dr Siddhartha Sharma


Hello, Dr. Sharma, and thank you for your question. You were absolutely correct, you cannot generate accurate coagulation results from an EDTA specimen, a problem that occasionally affects reference laboratories. In particular the PT and PTT results are markedly prolonged, and factor levels are markedly reduced. The issue is addressed in Adcock-Funk DM, Lippi G, Favaloro EJ. Quality standards for sample processing, transportation, and storage in hemostasis testing. Semin Thromb Hemost 2012;38: 576–85, and is reflected in the CLSI H21-A5 standard. I hope this helps.

By George Fritsma
Aug 3, 2015 2:08pm
George posts for Dr. Sharma:
Hi George, Thanks for the link to a very informative article. Read the same with interest and gained some useful insights regarding quality standards in hemostasis testing. A query though: Why does the Factor VII activity show no significant change in EDTA samples vis a vis other coagulation factors which show a minimal to marked decrease in their activities. Thanks, Dr Siddhartha Sharma.

Hi, Dr. Sharma, it appears that the PT is less prolonged by EDTA than the PTT. The clot-based factor VII assay is based on the PT, thus the results, though unreliable, are somewhat less affected than assays performed using the PTT. I hope this answers your question.
By Dr Emmanuel Favaloro
Aug 14, 2015 6:07am
Hi George & Siddhartha,

You may be interested in what happens when laboratories unknowingly test a normal EDTA sample, as opposed to a normal citrate plasma sample. We sent labs a series of samples, including normal EDTA, normal serum, normal heparinised sample, etc, as part of an EQA exercise over a decade ago. For the normal EDTA sample, 68% of labs falsely identified an inhibitor to factor V and/or FVIII. Only one lab correctly identified the sample as a normal EDTA sample. Other interpretations included fibrinogen defects/thrombin inhibitor, FV and/or FVIII deficiency and/or liver disease and LA. We published this study in two papers: Favaloro EJ, Bonar R, Duncan E, Earl G, Low J, Aboud M, Just S, Sioufi J, Street A, Marsden K (on behalf of the RCPA QAP in Haematology Haemostasis Committee). Identification of factor inhibitors by diagnostic haemostasis laboratories: A large multi-centre evaluation. Thrombosis and Haemostasis, 2006; 96: 73-78. and Favaloro EJ, Bonar R, Duncan E, Earl G, Low J, Aboud M, Just S, Sioufi J, Street A, Marsden K (on behalf of the RCPA QAP in Haematology Haemostasis Committee). Mis-identification of factor inhibitors by diagnostic haemostasis laboratories: recognition of pitfalls and elucidation of strategies. A follow up to a large multicentre evaluation. Pathology, 2007; 39: 504-511. The EDTA knocks out the Ca dependent pathways, and most notably FV & FVIII activity. Don't ever accept EDTA samples for coag testing--the patient will quite likely be falsely identified as having a coagulopathy that will cause much angst, and follow up testing/blood-letting that will please no one.

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