A patient is admitted through the hospital emergency department with thrombosis, and heparin is initially begun. Her baseline PTT, before heparin therapy, is prolonged at 68 seconds

Further laboratory studies determine that she has the lupus anticoagulant. What test should be used to monitor her heparin therapy?

a. PTT
b. PTT after first adding antithrombin to her plasma
c. Chromogenic anti-Xa assay
d. TT after first making a 1:10 dilution of the patient plasma


ANS: C
The PTT is already prolonged by the lupus anticoagulant, so the heparin therapeutic range for the PTT reagent becomes meaningless. In this case a chromogenic anti-Xa assay should be used.

Health Professions

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