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07-04-2010 | Cardiology | Article

Discard tubes unnecessary for coagulation blood tests


Free abstract

MedWire News: Discard tubes are unnecessary when drawing blood samples for coagulation testing, US researchers have found.

Current guidelines from the Clinical and Laboratory Standards Institute recommend drawing and discarding a tube of blood before collection of samples for coagulation testing, despite the evidence for the value of this being circumstantial at best, explain Kristi Smock (ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, Utah) and co-workers.

Following studies showing this is unnecessary for prothrombin time and partial thromboplastin time assays, the team examined whether a discard tube is necessary when measuring levels of fibrinogen, D-dimer, proteins C and S, antithrombin, and factors (F)VIII, IX, and XI.

The researchers compared levels of the coagulation markers in two consecutive blood samples taken from 30 healthy individuals and 30 participants using warfarin.

Analysis showed that none of the coagulation marker results significantly differed between the first and second tubes of blood in the healthy individuals or warfarin users. Indeed, most first and second tubes agreed to within a 10% difference and just 2% had greater than a 15% difference.

The first and second tubes of blood produced comparable results regardless of whether the individual had low, normal, or elevated levels of the coagulation markers being examined, Smock et al add in the journal Blood Coagulation & Fibrinolysis.

“This is the first study to evaluate the level of agreement between the first and second tube drawn for a variety of functional assays for coagulant and anticoagulant factors in both normal and abnormal (warfarinized) individuals,” the researchers write.

“Our data suggest that drawing a discard tube is not necessary for specialized coagulation testing,” they conclude.

MedWire ( is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

By Lynda Williams

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