At a Glance

Acquired factor IX deficiency can occur in a number of situations. One possibility is the presence of a spontaneously developed specific inhibitor to factor IX. Such an antibody can also appear in a patient with hemophilia B (factor IX deficiency) following treatment with factor IX, either prophylactically or to treat a bleeding episode. In this situation, the patient already has factor IX deficiency, but it can be made more severe by the presence of an antibody to factor IX.

Factor IX deficiency can also be acquired in patients who have vitamin K deficiency. In this situation, there is also an accompanying deficiency of factor II, factor VII, factor X, protein C, and protein S. All of these factors are vitamin K dependent for synthesis of the functional protein. Because the effect of warfarin is to inhibit the action of vitamin K, factor IX deficiency is also acquired as part of the therapeutic response to warfarin.

Factor IX can be decreased with many of the other coagulation factors in patients with severe liver disease. Factor IX can also be consumed in active clotting. Therefore, patients in disseminated intravascular coagulation (DIC) who were tested while factor consumption is active can show decreased levels of factor IX.

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

A prolonged partial thromboplastin time (PTT) in the presence of a low factor IX level confirms the presence of factor IX deficiency. Some patients with hemophilia B will develop inhibitors on exposure to factor IX. As noted, in these patients, there is already a congenital deficiency of factor IX but the deficiency is worsened by the presence of a neutralizing antibody to factor IX. Acquired factor IX deficiency can be differentiated from a simple congenital factor IX deficiency (i.e., hemophilia B) by a number of ways.

Hemophilia B patients typically have bleeding from early childhood, whereas patients with acquired factor IX deficiency do not typically show a lifelong history of bleeding. Another clue for an acquired factor IX deficiency is the presence of a known cause for the factor IX deficiency, such as vitamin K deficiency, initiation of warfarin therapy, or the development of DIC.

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?

The presence of a lupus anticoagulant can result in a low factor IX level that is not a true deficiency. The lupus anticoagulant produces an in vitro inhibition of the clotting reaction required to measure the factor IX level. In these cases, patients can usually be identified as having a lupus anticoagulant, instead of a truly low factor IX, by demonstrating the presence of a positive lupus anticoagulant test. In addition, in patients with a lupus anticoagulant, a low factor IX is often accompanied by low values for factor VIII, factor XI, and/or factor XII, along with the positive lupus anticoagulant test. Low factor IX levels in patients with a lupus anticoagulant are not associated with an increased risk for bleeding.

What Lab Results Are Absolutely Confirmatory?

The presence of a low factor IX level that has not been present from birth or a low factor IX level in a hemophilia B patient that has been decreased following exposure to a product containing factor IX are both indicative of a factor IX deficiency. An indication that an inhibitor to factor IX has arisen is a poor hemostatic response to infusion of factor IX that was previously effective in controlling a bleeding episode.