LabMed

High Molecular Weight Kininogen Deficiency – Acquired

At a Glance

Acquired high molecular weight kininogen (HK) deficiency is extremely rare. Antibody Baltimore is an antibody to factor XI that blocks high molecular weight kininogen binding and factor XIIa activation of factor XI (Blood 72:1748, 1988). It was associated with urinary tract bleeding. This antibody is to factor XI, not HK. Antibodies to HK itself should not be associated with bleeding.

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

A number of tests could be performed. The partial thromboplastin time (PTT) and a HK assay, along with evidence on a mixing study showing that that something in patient's plasma interferes with HK activity in vitro. (Table 1)

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?

Anticoagulants like unfractionated heparin, enoxiparin, fondparinux, hirudin, argatroban, bivalirudin, and dabigatran will interfere with any coagulant-based assay.

What Lab Results Are Absolutely Confirmatory?

A low HK assay with evidence that patient plasma, when mixed with normal plasma, specifically inhibits HK activity.

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

The requested tests to evaluate for an inhibitor to HK is not a clinical laboratory study. It should be done in a research laboratory interested in this area. Western blot of patient plasma showing HK antigen with no activity is a confirmatory assay.

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?

Anticoagulants will interfere with the HK assay and the inhibitor assay. Also, high plasma lipid states and high serum bilirubin may also present an interference.

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