Discard tubes are not necessary when drawing samples for specialized coagulation testing

Abstract

Discard tubes have traditionally been obtained when drawing samples for coagulation testing to avoid potential tissue factor activation of coagulation in the first tube that may lead to inaccurate results. Although discard tubes are no longer required for prothrombin time and partial thromboplastin time, the practice is still recommended for other coagulation studies due to lack of sufficient evidence that discard tubes are not needed. The objective of the present study was to determine whether the first citrate tube drawn can be used for special coagulation testing. We performed testing for fibrinogen, D-dimer, factors VIII, IX, XI, proteins C and S, and antithrombin on 30 healthy individuals and factors II, VII, IX, X, and proteins C and S on a second group of 30 healthy individuals and 30 individuals receiving warfarin. Testing was performed on two consecutive samples to evaluate the level of agreement between the two tubes. Paired t-testing showed no statistically significant differences between tube 1 and tube 2 for any of the tests performed. Most data pairs (tube 1, tube 2) agreed within 10% difference or less, and no positive or negative biases were observed. To our knowledge, this study is the first to evaluate the need for discard tubes in a variety of coagulation tests using both normal and abnormal samples. Our data suggest that discard tubes are not necessary when drawing samples for specialized coagulation testing.

The order of draw: much ado about nothing?

“… and Smock et al . concluded the same for specialized coagulation testing. Interestingly, Raijmakers et al .…”

Pre-analytical issues in the haemostasis laboratory: guidance for the clinical laboratories

“…Published studies have demonstrated that for routine coagulation testing, the use of a discard tube is not necessary because there was no significant difference in the aPTT and PT results between the first and second tubes drawn [2, 4, 5, 36, 44, 54]. Some studies evaluated the need for discard tubes in a variety of others coagulation tests (e.g.…”

“…Some studies evaluated the need for discard tubes in a variety of others coagulation tests (e.g. fibrinogen, D-dimer, factors II, V, VII, VIII, IX, X, XI, proteins C and S and AT, …) and suggested that discard tubes are not necessary when drawing samples for specialized coagulation testing [2, 5, 54, 55]. There are no data to support the need for a discard tube for specialized haemostasis assays [5].…”

Are there sufficient standards for the in vitro hemocompatibility testing of biomaterials?

“…Despite recent studies question the necessity of a discard tube, it is further noted that the first 3 -4 mL of blood are not suitable for testing due to the potential coagulation activation by e.g. tissue factor (thromboplastin) in the syringe [72][73][74]. Subsequent to the blood withdrawal and prior to the final test, blood samples should rest for at least 30 minutes under mild agitation, since platelet function, particularly platelet aggregation can be reduced immediately after blood collection [75].…”