Coagulation – part 4 – Partial Thromboplastin Time (PTT)
- The blood sample is taken in the anticoagulant.
- For PTT blood sample is 1.8 ml blood and anticoagulant (maybe ESR solution) 0.2 ml.
- Blood 1.8 ml + 0.2 ml ESR solution.
- Used to monitor the heparin therapy and control its dose.
- It is part of the coagulation panel workup.
- It evaluates:
- Extrinsic Pathway.
- Common Pathway.
- Advised to evaluate abnormal bleeding.
- It is advised before the surgery.
- It evaluates factors I, II, V, VIII, IX, X, XI, and XII (1, 2, 5, 8, 9, 10, 11, 12).
- To understand the coagulation mechanism, just go through the following diagram which gives the various coagulation factors and their role.
- PTT is a one-stage test.
- PTT serves the same function as APTT but APTT is more sensitive.
- PTT detects the intrinsic pathway deficiency of the thromboplastin system and common pathway.
- PTT also finds a defect in the extrinsic pathway.
- PTT screen intrinsic pathway and test for the adequacy of factor XII, XI, IX, and VIII.
- This compared with the normal control which may vary from lab to lab.
- Mostly with control maybe 25 to 35 seconds.
ABNORMAL PTT HIGH results are due to:
- Disseminated intravascular coagulopathy (DIC).
- Factor XII deficiency.
- Haemophilia A and B.
- Von Willebrand’s disease.
- Please for more details see in APTT and PT