Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (408 page)

   VTE following minimal or no provocation

   VTE at an unusual site (upper extremity, mesenteric vein, cerebral vein)

   Pulmonary embolism (PE) without obvious etiology

   Neonatal purpura fulminans

   Warfarin-induced skin necrosis

B.   Arterial thrombophilia

   Patients with unexpected/unexplained arterial thrombotic events.

  2.  Suspect acquired hypercoagulability

   Patients with unprovoked venous or arterial thromboembolism in the absence of a known family history. Some patients may have both venous and arterial thrombotic events.

   Laboratory Findings

When should inherited thrombophilia tests be performed, in whom, and which tests?

There is no urgency in obtaining thrombophilia tests for patients who present with an acute venous thromboembolism (VTE), because this information does not alter acute therapy decisions. Consider obtaining a thrombophilia workup, if indicated, when the patient has recovered from the acute event and ideally when warfarin and/or heparin administration have been discontinued for at least 2–4 weeks.

I.     
Suspected inherited thrombophilia
.

   
Testing for inherited thrombophilia serves only a limited purpose and should not be performed on a routine basis: patients who have had one episode of VTE and have thrombophilia are only at a slight risk of recurrent events.

   
Exceptions are to identify asymptomatic immediate family members of patients with VTE who test positive for thrombophilia.

A.   Venous thrombophilia: The most common causes of inherited venous thrombophilia are the factor V Leiden and the prothrombin gene mutations. Protein C and S deficiencies, antithrombin deficiency, and dysfibrinogenemia are very rare. Elevated factor VIII coagulant activity is now accepted as an independent marker of increased risk for thrombosis.

   
First-tier tests.
^†††

•   Activated protein C resistance (APCR): functional assay

•   Prothrombin G20210A: genetic assay

•   Protein C activity
^‡‡
: functional assay

•   Protein S activity functional assay

•   Antithrombin (AT) activity: functional assay

   
Second-tier tests.