Will Excedrin Interfere with Protein C Testing?
No, taking Excedrin (acetaminophen, aspirin, and caffeine) will not interfere with protein C testing. The components of Excedrin do not affect the laboratory assays used to measure protein C levels or function.
Why Excedrin Does Not Interfere
Protein C assays measure specific coagulation pathway components that are unaffected by acetaminophen, aspirin, or caffeine 1.
The primary interferences with protein C testing include anticoagulants (warfarin, heparin, direct thrombin inhibitors, direct factor Xa inhibitors), lupus anticoagulants, factor deficiencies, and elevated factor VIII levels—none of which are caused by Excedrin components 1.
Aspirin's antiplatelet effects do not impact protein C measurement, as protein C testing evaluates the vitamin K-dependent anticoagulant pathway, not platelet function 1.
Optimal Timing for Protein C Testing
Test when the patient is not acutely ill or thrombosed, as acute thrombosis can transiently lower protein C functional levels 2.
Avoid testing during anticoagulation therapy with warfarin, heparin, or direct oral anticoagulants, as these medications can significantly interfere with results 1, 2.
For patients with family history of protein C deficiency, testing can proceed regardless of recent Excedrin use, as the components do not affect the vitamin K-dependent protein C pathway 1.
Clinical Context for This Patient
Given the family history of protein C deficiency, this 19-year-old male should undergo testing to determine his thrombotic risk profile 1.
Heterozygous protein C deficiency does not always cause thrombotic complications—in one family study, only 2 of 16 protein C-deficient members experienced thromboembolic disorders 3.
Testing should include both protein C antigen and functional activity to properly classify the deficiency type 4.
Important Caveat
- The patient can continue using Excedrin for headache management without concern for test interference, though limiting use to no more than twice weekly prevents medication-overuse headache 5.