Determination of Clotting Time

Aim: To determine the clotting time of own blood by the capillary method. 

Requirements:  Sterile disposable needle (26G), 10-12 cm long clean capillary tube with uniform bore diameter of 1-2 mm, stopwatch, cotton swab, 70% alcohol, or any other suitable marketed antiseptic. 

Principle:  Clotting or coagulation is a complex process in which clotting factors activate each other and form a gel-like substance of insoluble fibrin threads. This process is very important as it prevents excessive blood loss irrespective of the reason for the bleeding. The process occurs in three  stages:

  • Formation of prothrombin activator or prothrombinase (combination of activated clotting factors V and X) by intrinsic and extrinsic pathway (an injury to blood vessel and tissues respectively).
  • Conversion of prothrombin (clotting factor II) into the enzyme thrombin by prothrombinase.
  • Conversion of soluble fibrinogen (clotting factor I) into insoluble fibrin by thrombin;  fibrin forms the threads of the clot. 

Clotting time is the interval between the entry of blood into the glass capillary tube and the formation of thin fibrin threads. The clotting time is commonly determined by: 

  1. Capillary blood clotting time method (Wright’s method). 
  2. Drop method. 
  3. Venous blood clotting time method. 


  1. Select the appropriate finger, usually the ring finger, and clean the tip of the finger using  70% alcohol or any other suitable antiseptic. 
  2. Get a finger prick using a sterile disposable needle (26G) to obtain free-flowing blood with minimum pain. 
  3. Immediately, start the stopwatch and note the time. 
  4. Dip one end of the capillary tube in blood, the blood will rise in the tube by capillary action which can be enhanced by keeping its open end at a lower level as shown in Fig.1. 
  5. Note the time when blood starts to enter the capillary tube as zero time. 
  6. Hold the capillary tube between the palms of your hands to keep the blood near body temperature. 
  7. Gently break off approximately 1 cm bits of the capillary tube from one end at intervals of 30 seconds and observe for the formation of fibrin thread of a minimum 5 mm length between the broken ends of the capillary tube. This is called rope formation. Note the time.
Determination of Clotting Time

Note: The normal clotting time by a capillary method is 3-6 minutes 


  • Name: 
  • Age: 
  • Gender: 
  • Date: 
  • Time of pricking: 11:00:00 am 

(An example for writing observation is given below) 

Sr.  No.Timing of breaking capillary piecesFormation of fibrin thread  (Yes/No)
1.11:01:00 amNo
2.11:01:30 amNo
3.11:02:00 amNo
4.11:02:30 amNo
5.11:03:00 amNo
6.11:03:30 amNo
7.11:04:00 amYes

The fibrin thread was observed between broken ends of the capillary tube after ‘x’ minute and ‘y’ seconds. 

Result: Clotting time of own blood was found to be ‘x’ minutes and ‘y’ seconds.

Clinical Significance: 

Sr.  No.Clotting timeIndications/Factors responsible
Malnutrition and parturition
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