Should an accelerated APTT result be canceled for being clotted, even in the absence of a visible clot?

Q. Should an accelerated APTT result be canceled for being clotted, even in the absence of a visible clot?

A.If an activated partial thromboplastin time is accelerated but a clot is not visible in the sample, the sample should be reinspected for the presence of a clot and a redraw for repeat testing should be considered. In the appropriate clinical context (such as previous thromboembolic events, cancer, or pregnancy) and if the accelerated results can be reproduced, an accelerated APTT can be reported.^1,2 These scenarios are uncommon and should be considered on a case-by-case basis.

An accelerated APTT result from a sample with a visible clot should be canceled.

Tripodi A, Chantarangkul V, Martinelli I, Bucciarelli P, Mannucci PM. A shortened activated partial thromboplastin time is associated with the risk of venous thromboembolism. Blood. 2004;104(12):3631–3634.

Lippi G, Salvagno GL, Ippolito L, Franchini M, Favaloro EJ. Shortened activated partial thromboplastin time: causes and management. Blood Coagul Fibrinolysis. 2010;21(5):459–463.

Clarence Chan, MD, PhD
Fellow, Clinical Chemistry
Department of Pathology
University of Chicago
Chicago, Ill.
Junior Member, CAP Hemostasis and Thrombosis Committee