Clinical Utility of Testing

The Pt 20210G^A mutation has been associated with a 2- to 3-fold increased risk of VTE incidence. The VTE risk among Pt 20210G^A carriers is compounded by deficiency of AT, PC, or PS, or by Factor V Leiden. Women with the Pt 20210G^A mutation who are taking oral contraceptives have a 16-fold increased risk for deep vein thrombosis or pulmonary embolism, and a 150-fold increased risk of cerebral vein thrombosis. While the VTE risk among individuals homozygous for the Pt 20210G^A mutation is likely higher than the risk among heterozygotes, this mutation is a relatively weak risk factor compared to deficiency of PC or PS. Compared to noncarriers with VTE, the risk of recurrent VTE does not appear to be increased for individuals heterozygous for the Pt 20210G^A mutation. However, the risk of recurrence is increased for individuals with both a heterozygous Pt 20210G^A mutation and Factor V Leiden.

Available Assays

Although Pt 20210G^A carriers have statistically higher plasma prothrombin activity, the normal range for plasma prothrombin activity is quite broad. Thus, plasma prothrombin activity cannot accurately distinguish Pt 20210G^A carriers from noncarriers and is not of value for diagnosis. Direct DNA testing for the specific mutation is required for diagnosis. Molecular testing methods available for the Pt 20210G^A mutation are essentially the same as for Factor V Leiden. Each laboratory must ensure that its method can distinguish the Pt 20210G^A from an uncommon polymorphism at nucleotide 20209 (C^T). In 2003, Roche Diagnostics Corporation (Indianapolis, IN) obtained FDA approval for in vitro diagnostic test kits for Factor V Leiden and the prothrombin 20210G^A gene mutation. Recommendations for prothrombin 20210G^A mutation testing and management are essentially the same as for Factor V Leiden.

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