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.

Indications

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 recommended 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, go through the following diagrams, which give the various coagulation factors and their role.
   

   Summary of the coagulation pathways

   

   Prothrombin leading to stable clot formation

Coagulation hemostasis mechanism

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 screens intrinsic pathways and tests for the adequacy of factors XII, XI, IX, and VIII.
      

      Principle of PTT (Partial thromboplastin time)

Normal

• This is compared with the normal control, which may vary from lab to lab.
• Mostly with control, maybe 25 to 35 seconds.
  Effects of various anticoagulants on Partial thromboplastin test (PTT) :

  Various anticoagulants	Effects of various anticoagulants on PTT
  Heparin	Increased
  Urokinase	Increased
  Streptokinase	Increased
  Aspirin	Normal
  Warfarin	Normal
  Dipyridamole	Normal
  Sulfinpyrazone	Normal

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.
                     APTT and PT interpretations:
   

   APTT and PT interpretations

• Please, for more details, see in APTT and PT