The Diagnostic Pitfall: DOACs and Activated Partial Thromboplastin Time
Mohamed Hanafy Morsy, Associate Professor of Clinical Pathology, Hematopathologist at Makkah Health Cluster, posted on LinkedIn:
”Lab staff + Cardiology Colleagues – Quick 30-second read that will save you confusion forever
The Diagnostic Pitfall: Direct Oral Anticoagulants (DOACs) and Activated Partial Thromboplastin Time (aPTT)
Scenario: A patient is receiving therapeutic anticoagulation with a direct Factor Xa inhibitor (e.g., Apixaban, Rivaroxaban). Routine or emergent coagulation screening returns an aPTT result that is unmeasurably short, <25 seconds, or within the institutional reference interval.
Your reaction?
A) Panic – “The patient has NO anticoagulation”
B) Call the lab – “Your machine is broken”
C) Relax – This is 100 % normal and expected
The correct answer is C
Apixaban (and all DOACs) have minimal to no effect on aPTT.
A super-low aPTT does NOT mean the drug isn’t working.
Ideal lab comment to add automatically when apixaban is on the chart:
“The aPTT result is not validated for assessing the efficacy of Direct Factor Xa Inhibitors. If quantitative assessment of drug concentration is required, order the drug-specific Chromogenic Anti-Xa Assay.”
Let’s stop the 2 a.m. pages to hematology for this.”
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