Laboratory Management of the Bleeding Patient

Laura J Taylor

doi:10.29074/ascls.16.2.111

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Laura J Taylor, MT(ASCP)⇑
1. is a medical technologist at the University of Alabama at Birmingham, Birmingham AL

Address for correspondence: Laura J Taylor MT(ASCP), Department of Pathology, 619 South 19th Street, West Pavilion, P230, University of Alabama at Birmingham, Birmingham AL 35233. http://uabcoag.net

Extract

From the laboratory point of view, test results are only as reliable as the quality of the sample. It is imperative that the specimens received for coagulation testing are collected by a clean venipuncture with as little trauma to the tissues as possible. Clotted, hemolyzed, and contaminated specimens are not suitable and should not be used by the laboratory. The most common causes of erroneous results are related to the blood draw; therefore, special care must be taken to avoid any undue problems. Sodium citrate is the anticoagulant that is most commonly used for both routine and special coagulation testing. The citrated blood should be spun by routine centrifugation methods so that platelet free plasma is obtained.¹

PROTHROMBIN TIME The prothrombin time (PT) monitors the factors that are in the extrinsic pathway – factors VII, X, V, and II. A PT is performed by adding synthetically prepared tissue factor, generally from brain or lung, and calcium to the test plasma and measuring the time it takes the clot to form. Prolongation of the PT is most often a result of deficiencies in factor VII but can also be caused by any of the aforementioned factors. Decreased fibrinogen, levels less than 100 mg/dL, will also prolong the PT; however, this test is not used to measure fibrinogen deficiency since most coagulation labs can perform a fibrinogen assay.¹

ACTIVATED PARTIAL THROMBOPLASTIN TIME The partial thromboplastin time reagent is a preparation of synthetic phospholipids, particulate activator, and calcium. The APTT, or simply PTT,…

ABBREVIATIONS: APTT = activated partial thromboplastin time; DIC = disseminated intravascular coagulation; PT = prothrombin time; PTT = partial thromboplastin time; TCT = thrombin clotting time; vWD = von Willebrand disease; vWF = von Willebrand factor.