Object:
To determine the clotting time of blood.
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Requirements:
Sterilized needle; small test-tubes, stop watch water bath, syringe and glass slides.
Principle and procedure:
It is the time taken for blood to clot in vitro at a standard temperature, or it is the length of time from the moment blood is collected till the appearance of clotting.
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Following three methods are used for counting the clotting time of blood.
A. Note the time, then take 1 ml venous blood in a small test- tube, put the tube in a water bath at 37°C. Every 30 seconds shake the tube and tilt it slowly.
Note the time when blood stops flowing in the tube and its surface line no longer changes on tilting. The time taker, is the clotting time, it is normally 5 to 10 minutes.
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B. Take 5 ml venous blood in a syringe and start a stop watch. Put 1 ml of blood in each of two small equal-sized test tubes, put the tubes in a water bath at 37°C.
After some time tilt the tubes every half minute, when the tube can be tilted through 90° or even inverted without spilling the blood then the blood has coagulated, note the time.
C. Put a drop of blood on a clean slide and note the time. Every half minute pull a clean needle slowly through the drop of blood.
When a fine thread of fibrin can be pulled up by the point of the needle, then coagulation has started, note the time.