## Coagulation Factor Deficiencies
- **Contact pathway factor deficiencies**: Deficiencies in factors XII, XI, IX, or VIII can lead to prolonged PTT[2]. These are involved in the intrinsic coagulation pathway.
Deficiency of clotting factors: Conditions like hemophilia A or B, where specific clotting factors are deficient1.
- **Other coagulation factor deficiencies**: Low levels of factors II, V, or X can also result in prolonged PTT[2].
## Acquired Conditions
- **Antiphospholipid antibodies**: This is the most common cause of prolonged PTT in outpatients, accounting for about 22.6% of cases[2].
- **Vitamin K deficiency or liver disease**: These conditions can impair the production of clotting factors, leading to prolonged PTT in approximately 11.6% of cases[2].
- **Heparin therapy**: PTT is commonly used to monitor heparin anticoagulation, and therapeutic levels of heparin will prolong the PTT[3].
## Other Causes
- **Lupus anticoagulant**: This can interfere with phospholipid-dependent coagulation tests, causing PTT prolongation[3].
- **Von Willebrand disease**: Some types of this bleeding disorder can affect factor VIII levels and prolong PTT[3].
- **Specific factor inhibitors**: Antibodies against individual clotting factors can develop and cause prolonged PTT[1].
## Idiopathic Cases
In about 22.1% of outpatients with prolonged PTT, a definite cause may not be identified despite extensive testing[2].
It's important to note that prolonged PTT doesn't always indicate an increased bleeding risk. In fact, some causes like antiphospholipid antibodies are associated with thrombotic risk rather than bleeding[2]. Proper investigation of prolonged PTT typically requires multiple additional tests to determine the underlying cause and its clinical significance.
Citations:
[1] https://www.ncbi.nlm.nih.gov/books/NBK507772/
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6782020/
[3] https://www.testing.com/tests/partial-thromboplastin-time-ptt-aptt/
[4] https://medlineplus.gov/lab-tests/partial-thromboplastin-time-ptt-test/
[5] https://www.sciencedirect.com/topics/medicine-and-dentistry/partial-thromboplastin-time