The following results were found in a 28-year-old woman as part of a work up for infertility. She has never had a history of bleeding or bruising nor does she have a family history for bleeding.
- What are the causes of an elevated PTT in a non-bleeding patient?
- Describe the additional tests that would be required to make a diagnosis in this case.
- What is a lupus anti-coagulant and how does it alter the PTT?
The PTT (partial thromboplastin time) measures the intrinsic and common pathways in the coagulation cascade. By understanding the methodology of testing and the factors inherent in the cascade, a differential for non-bleeding patients can be made:
- Sample error (including heparin contamination of the phlebotomy site if a heparinized tube was used prior to the citrate/ coagulation tube)
- Anti-phospholipid antibody
- Heparin use
- Factor XII deficiency (no association with clinical bleeding)
- HMWK or kallikrein deficiency (not associated with in vivo bleeding)
The 50:50 mix is a test used to identify if the patient has a deficiency in a factor versus an inhibitor. It entails mixing a sample of patient with normal plasma. Full correction in the PTT indicates a factor deficiency. A lack of correction indicates an inhibitor.
If the inhibitor is present, it is important to rule out a lupus anticoagulant. Typically a dilute Russell’s viper venom time (dRVVT) is used for confirmation.