Factor X Deficiency – Acquired

At a Glance

Patients with factor X deficiency can experience a new onset of bleeding, such as epistaxis, gastrointestinal hemorrhage or hematuria, in someone without a lifelong personal or family history of a bleeding disorder, whose laboratory evaluation shows normal platelet count and function but prolonged prothrombin time (PT) and partial thromboplastin Time (PTT).

If the patient has confirmed or suspected amyloidosis, factor X deficiency is more likely than deficiencies of the other common pathway factors, that is, V, II or fibrinogen, because of the amyloid fibrils bind factor X from the plasma. Rarely, acquired factor X deficiency is due to an inhibitor to the factor that can be associated with respiratory tract infections, burns or leprosy. Acquired factor X deficiency has also been seen with a lupus anticoagulant with specificity for this factor.

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

The first test is a factor X activity assay. If the result confirms factor X deficiency, performing a PT or PTT mixing study helps determine if the low factor X is due to a simple deficiency or an inhibitor. If the mixing study shows correction of the initially abnormal test (PT or PTT), an inhibitor is excluded. If the mixing study fails to correct the clotting time, an inhibitor may be detected and quantitated by the Bethesda assay. It may also be appropriate to request a test for lupus anticoagulant, since these antibodies rarely bind to factor X and lower its concentration in the plasma. (Table 1)

Table 1

Test Results Indicative of the Disorder
prolonged prolonged

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?

There are no medications that could cause a falsely abnormal result. However, warfarin antagonizes vitamin K, blocking the synthesis of normal factor X as well as the other vitamin K-dependent factors II, VII and IX. Other drugs, such as antibiotics, that cause vitamin K deficiency also have the same effect.

What Lab Results Are Absolutely Confirmatory?

Factor X assay, which shows low result, is confirmatory.

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

Evaluation of the patient for amyloidosis with serum and urine protein electrophoresis may be appropriate in patients with isolated deficiency of factor X, since amyloidosis is most commonly a complication of a plasma cell dyscrasia. In the presence of monoclonal proteins in serum and/or urine, a bone marrow examination should follow to determine the degree of involvement by plasma cells. Since renal involvement by amyloidosis may cause nephrotic syndrome, urinalysis should be ordered to assess for the presence of proteinuria.

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