Prothrombin (Factor II) Deficiency - Congenital

At a Glance

The diagnosis of congenital factor II deficiency is suggested by a lifelong history of mild to moderate bleeding in patients with prolonged prothrombin time (PT) and partial thromboplastin time (PTT). These include hemarthroses and intracranial bleeding, easy bruising, and postoperative bleeding.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

Tests consistent with a diagnosis of congenital factor to deficiency include:

  • Prolonged PT and PTT; Normal thrombin time.

  • Correction of the 1:1 mixing study for the PT and PTT

  • Isolated decrease in factor II activity

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

Acquired prothrombin deficiency is seen in patients with liver disease, vitamin K deficiency (malnutrition, antibiotics), or ingestion of vitamin K antagonists, such as warfarin or superwarfarins. In all of these conditions, all vitamin K-dependent factors, including protein C and protein S, are decreased.

What Confirmatory Tests Should I Request for My Clinical Dx? In addition, what follow-up tests might be useful?

An inherited etiology is supported by the presence of a childhood history of bleeding, positive family history (autosomal recessive inheritance), and, if necessary, mutation analysis of the factor II gene. Heterozygous individuals usually have factor II activity near 50%, homozygous—less than 30%. Bleeding complications are more likely to occur with a factor II level less than 10%.

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