Workup for Elevated PT with Normal INR and Normal PTT
Understanding the Discrepancy
This scenario represents a technical/reporting artifact rather than a true coagulopathy, and the key is recognizing that a normal INR mathematically contradicts an elevated PT. The INR is calculated directly from the PT using the formula INR = (PT patient/PT normal)^ISI, so if the INR is truly normal (0.9-1.1), the PT cannot be simultaneously elevated 1, 2, 3.
Immediate Steps
Verify the Laboratory Results
Request immediate repeat testing of both PT and INR on the same sample to confirm the discrepancy, as this pattern suggests either a reporting error, incorrect reference range, or ISI calibration issue 2, 3.
Check if your laboratory is reporting PT in seconds versus PT ratio, as PT of 16.4 seconds may actually be within normal range depending on the specific thromboplastin reagent used (normal ranges vary from 11-16 seconds) 1, 3.
Verify that the INR calculation is appropriate for your clinical context—INR is only valid for patients on vitamin K antagonists and should not be used to interpret PT in other settings 1, 2, 3, 4.
Rule Out Preanalytical Issues
Confirm proper sample collection technique, as underfilled tubes, delayed processing, or contamination with heparin can artifactually prolong PT 5, 6.
Document any anticoagulant exposure including heparin, direct oral anticoagulants, or warfarin, as these can affect PT measurement 1, 5.
Clinical Assessment
Evaluate for Bleeding Risk
Obtain detailed personal bleeding history focusing on prior surgeries, dental extractions, menstrual bleeding, easy bruising, and spontaneous bleeding episodes, as the absence of bleeding history with normal PTT makes clinically significant coagulopathy extremely unlikely 6.
Document family history of bleeding disorders, as this is the strongest predictor of underlying coagulopathy (P < 0.001) 6.
If both personal and family bleeding histories are negative AND repeat PT/INR normalize, the negative predictive value exceeds 95% and no further workup is needed 6.
Diagnostic Algorithm Based on Repeat Testing
If Repeat Testing Shows Normal PT and INR
No further workup is required in patients without personal or family bleeding history, as this represents laboratory variability or preanalytical error 6.
Consider discharge with reassurance, as 68% of patients referred for abnormal coagulation profiles have normal repeat testing 6.
If PT Remains Elevated with Normal INR on Repeat
This pattern is physiologically impossible and indicates a laboratory reporting or calibration problem—contact your laboratory director to review ISI calibration and reference ranges 1, 2, 3.
Request PT be reported as both seconds and ratio (patient PT/mean normal PT) rather than relying on INR, as INR standardization fails outside the context of warfarin monitoring 3, 4.
If Both PT and INR Are Elevated on Repeat (with Normal PTT)
Perform mixing study (1:1 mix with normal pooled plasma) to differentiate factor deficiency from inhibitor 7.
If mixing study corrects immediately, measure factor VII level specifically, as isolated factor VII deficiency is the only single factor deficiency that prolongs PT without affecting PTT 7, 5.
If mixing study does not correct, consider lupus anticoagulant testing, though this typically also prolongs PTT 7, 5.
In patients with liver disease, PT should be reported as activity percentage rather than INR, as INR fails to standardize results in hepatic dysfunction 1, 4.
Special Considerations
Liver Disease Context
Traditional coagulation tests including PT/INR are inadequate and misleading in cirrhosis, as they only partially evaluate hemostasis and ignore counterbalanced procoagulant factors 1.
Normal LFTs make significant hepatic synthetic dysfunction unlikely, but consider viscoelastic testing (TEG/ROTEM) if procedural bleeding risk assessment is needed 1.
When to Pursue Further Testing
Only pursue factor assays or specialized coagulation testing if there is positive bleeding history (personal or family) or if repeat testing confirms true PT prolongation with appropriate INR correlation 6.
Avoid reflexive hematology consultation for isolated laboratory abnormalities without clinical correlation, as this leads to unnecessary testing and patient anxiety 6.
Common Pitfalls to Avoid
Do not use INR to interpret PT results in non-warfarin patients—the INR scale was designed exclusively for warfarin monitoring and is invalid in other clinical contexts 1, 2, 3, 4.
Do not delay necessary procedures based on a single discrepant laboratory value without clinical bleeding history 6.
Do not order extensive factor assays before confirming the abnormality on repeat testing and performing mixing studies 7, 6.
Remember that PT reference ranges vary significantly between laboratories and thromboplastin reagents—a PT of 16.4 seconds may be normal for your specific laboratory 1, 2, 3.