Coagulation – part 4 – Partial Thromboplastin Time (PTT)

Sample

1. The blood sample is taken in the anticoagulant.
2. 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.

Indication

1. Used to monitor the heparin therapy and control its dose.
2. It is part of the coagulation panel workup.
3. It evaluates:
   1. Extrinsic Pathway.
   2. Common Pathway.
4. Advised to evaluate abnormal bleeding.
5. It is advised before the surgery.
6. It evaluates factors I, II, V, VIII, IX, X, XI, and XII (1, 2, 5, 8, 9, 10, 11, 12).

Pathophysiology

1. To understand the coagulation mechanism, just go through the following diagram which gives the various coagulation factors and their role.

2. PTT is a one-stage test.
   1. PTT serves the same function as APTT but APTT is more sensitive.
3. PTT detects the intrinsic pathway deficiency of the thromboplastin system and common pathway.
   1. PTT also finds a defect in the extrinsic pathway.
   2. PTT screen intrinsic pathway and test for the adequacy of factor XII, XI, IX, and VIII.

Normal

• 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:

1. Cirrhosis.
2. Disseminated intravascular coagulopathy (DIC).
3. Factor XII deficiency.
4. Haemophilia A and B.
5. Hypofibrinogenemia.
6. Malabsorption.
7. Von Willebrand’s disease.

• Please for more details see in APTT and PT

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