How is the diagnosis of protein C deficiency confirmed?

Updated: Jan 04, 2019
  • Author: Shamudheen Rafiyath, MD; Chief Editor: Perumal Thiagarajan, MD  more...
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A decreased protein C activity level is required to make the diagnosis of protein C deficiency. However, owing to the broad normal ranges of protein C antigen and activity, diagnosis of heterozygous protein C deficiency can be challenging. Patients with levels less than 50% are likely to have a true hereditary deficiency, whereas levels between 55% and 65% may reflect heterozygous deficiency or the low end of the normal distribution. [15] A functional protein C assay should be employed for screening purposes, as it will identify both type I and type II defects. In the event of a low protein C activity, a reflexive immunologic assay should be performed to distinguish between these types.

As described in Causes, a number of conditions may result in acquired protein C deficiency. To the extent possible, laboratory testing should be performed in patients without a history of such causes to confirm that deficiency, when identified, is due to a genetic defect rather than an acquired cause. The timing of testing with respect to acute thrombosis and warfarin therapy deserves special mention.

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