What testing practice should be avoided when evaluating for hereditary Protein C, Protein S, or Antithrombin deficiencies?

What testing practice should be avoided when evaluating for hereditary Protein C, Protein S, or Antithrombin deficiencies?

• A. Testing during acute thrombosis.
• B. Testing while on anticoagulation.
• C. Testing after DOAC withdrawal.
• D. Testing in a stable state.

Answer: (B)

The key idea is that testing for hereditary deficiencies of Protein C, Protein S, or Antithrombin is highly susceptible to interference from anticoagulant therapy. Anticoagulants can directly alter the activity or levels of these natural anticoagulants, producing results that resemble a deficiency even when none is inherited. That makes testing while the patient is on anticoagulation unreliable for determining true hereditary deficiency. For example, warfarin lowers Protein C and Protein S levels, and heparin/DOACs can affect antithrombin activity or interfere with certain assays. Therefore, the practice to avoid is performing these tests while the patient is on anticoagulation. In contrast, ideally you test when the patient is not on anticoagulants and is in a stable state, or after an appropriate washout period if safe and feasible, to obtain an accurate assessment of inherited deficiency. Testing during an acute thrombotic event can also be misleading due to consumption, but the most consistent confounder to avoid is ongoing anticoagulation.

The key idea is that testing for hereditary deficiencies of Protein C, Protein S, or Antithrombin is highly susceptible to interference from anticoagulant therapy. Anticoagulants can directly alter the activity or levels of these natural anticoagulants, producing results that resemble a deficiency even when none is inherited. That makes testing while the patient is on anticoagulation unreliable for determining true hereditary deficiency. For example, warfarin lowers Protein C and Protein S levels, and heparin/DOACs can affect antithrombin activity or interfere with certain assays. Therefore, the practice to avoid is performing these tests while the patient is on anticoagulation.

In contrast, ideally you test when the patient is not on anticoagulants and is in a stable state, or after an appropriate washout period if safe and feasible, to obtain an accurate assessment of inherited deficiency. Testing during an acute thrombotic event can also be misleading due to consumption, but the most consistent confounder to avoid is ongoing anticoagulation.