Differential Diagnosis

Coumadin therapy in the therapeutic or supratherapeutic range

Moderate to severe vitamin K deficiency

Treatment with high doses of heparin or low molecular weight heparin

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Treatment with direct thrombin inhibitors, such as hirudin or related compounds (i.e., lepirudin, refludan) or argatroban

Moderate to severe DIC

Moderate to severe liver disease

A lupus inhibitor with an associated decrease in factor II or a lupus inhibitor strong enough to increase PT, as well as PTT

Suggested Additional Lab Testing

To assess the possibility of DIC, get D-dimer levels.

  • If D-dimers are elevated, measure platelet count and fibrinogen level.

Test for factors II, V, VII, and X to assess a PT prolongation.

Test for factors VIII, IX, XI, and XII to assess a PTT prolongation.

In liver disease, all the factors can be low, except factor VIII, which tends to become elevated because it can be synthesized outside the liver.

  • Obtain liver function tests, especially serum albumin, to determine if the PT and PTT abnormalities could be associated with decreased production of coagulation factors by the liver.

Get a value for PTT after the sample is treated with an enzyme that degrades heparin.

  • If PTT and PT normalize after removal of heparin from the sample, PT and PTT elevations are most likely associated with heparin or low molecular weight heparin treatment.

Do a lupus inhibitor test if there is no explanation for the PT and PTT prolongations from the previously mentioned tests.

  • Factor II level may be useful to accompany the lupus anticoagulant test, because some lupus anticoagulant patients have a low factor II, leading to a prolonged PT.