Phlebotomist: Coagulation Specimens

There are several important guidelines to follow when collecting coagulation specimens.

-It is no longer necessary to clear a needle of potential thromboplastin contamination by collecting a few milliliters of blood in a plain red top tube for PT or PTT tests. A clear tube should be used for all other coagulation tests.

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-For coagulation tests, sodium citrate tubes must be filled completely to obtain a 9:1 ratio of blood to anticoagulant. This ratio can become altered if the patient's hemoglobin level is abnormally high or low. If this is a concern, a special collection tube can be requested to have the anticoagulant volume adjusted. Blue top tubes are designed for fibrin degradation (FDP) or fibrin split products (FSP) and should not be used for coagulation tests because they contain different additives and have different volumes.

-Never try to combine two partially filled tubes together to obtain a full tube of specimen. The anticoagulant-to-blood ratio will not be more than necessary and will cause inaccurate results.

-Certain coagulation factors are less stable than others. For example factors V and VIII are not stable and should be centrifuged and plasma frozen if lab tests can not be performed on them in a timely manner and especially if the specimens are to be transported.

-Coagulation specimens that are drawn from an indwelling catheter must be drawn following very specific guidelines. About 5 mL of blood should be collected and discarded before the actual specimen is collected. If heparin was introduced into the catheter line than the line must be flushed with 5 mL of saline before the discard blood is collected and thrown out.