Unexpected Prolonged INR Before Elective Surgery
A 63-year-old woman is scheduled for elective laparoscopic cholecystectomy in 48 hours. Preoperative labs: PT 21.4 s (reference 11–13.5), INR 1.9, aPTT 38 s (reference 25–35), platelets 210 × 10^9/L, fibrinogen 320 mg/dL. She takes no warfarin, no antibiotics, and no herbal supplements. She has no bleeding history, no bruising, and no family history of bleeding. Liver enzymes are normal. She had a similar isolated PT prolongation 2 years ago that was never worked up. The surgeon asks whether to cancel the case.
1. Construct a differential for isolated PT prolongation in this patient, and state which tests you would order to distinguish the causes.
Read the worked answer
Differential for isolated PT prolongation (normal aPTT, normal platelets, normal fibrinogen):
- Factor VII deficiency (congenital or acquired) - factor VII has the shortest half-life (~4–6 h) and is the only factor in the extrinsic pathway; isolated PT prolongation with normal aPTT is classic. Congenital deficiency may be mild and asymptomatic.
- Early vitamin K deficiency or warfarin effect - but she denies warfarin; vitamin K deficiency usually also prolongs aPTT once factors II, IX, X fall. Early deficiency can affect VII first. Consider malabsorption, poor intake, antibiotic use (denied).
- Liver disease - synthetic dysfunction; but liver enzymes are normal and fibrinogen is normal, making this less likely.
- Lupus anticoagulant - usually prolongs aPTT, but some LA reagents are PT-sensitive; however, isolated PT prolongation is atypical.
- Factor VII inhibitor - rare, usually acquired with bleeding; she has no bleeding.
- Preanalytical/analytical - underfilled citrate tube (high citrate:blood ratio), hemolysis, lipemia, or a PT reagent/instrument issue. Must exclude first.
Tests to order:
- Repeat PT/INR with a properly filled 3.2% citrate tube (confirm preanalytical).
- Mixing study (1:1 with normal plasma): corrects → factor deficiency; does not correct → inhibitor.
- Specific factor VII activity assay.
- If VII low: factors II, IX, X, and von Willebrand factor to assess for combined deficiency; consider vitamin K status.
- Lupus anticoagulant testing (dRVVT, hexagonal phase) if mixing is abnormal.
- Review medications and diet for vitamin K.
2. The mixing study corrects the PT, and factor VII activity is 32% (reference 50–150%). How do you advise the surgeon, and what is the perioperative plan?
Read the worked answer
Interpretation: Correction on mixing indicates a factor deficiency, not an inhibitor. Factor VII activity of 32% is a mild deficiency (mild congenital factor VII deficiency is typically 10–40% and often asymptomatic).
Advice to surgeon:
- This is a mild, likely congenital factor VII deficiency. The patient has no bleeding history, which is reassuring, but factor VII levels do not correlate perfectly with bleeding risk.
- For a low-bleeding-risk procedure such as laparoscopic cholecystectomy, many patients with mild FVII deficiency and no bleeding history can proceed without factor replacement, but the plan should be individualized with hematology input.
- Do not cancel solely on the INR; the INR is a poor predictor of bleeding in isolated FVII deficiency because it is exquisitely sensitive to small changes in VII.
Perioperative plan:
- Hematology consultation.
- Confirm the diagnosis with repeat FVII activity and family studies if desired.
- If bleeding risk is judged significant, consider recombinant activated factor VII (rFVIIa) or fresh frozen plasma per hematology, but this is usually reserved for higher-risk procedures or patients with bleeding history.
- Avoid drugs that impair hemostasis (NSAIDs, aspirin) perioperatively.
- Monitor for bleeding postoperatively; have a low threshold for rechecking PT/INR and factor levels if bleeding occurs.
Key teaching point: An isolated PT prolongation with a normal aPTT should prompt a factor VII assay; the INR can be misleadingly high in mild FVII deficiency and should not by itself dictate surgical cancellation.