ESTIMATION OF CLOTTING TIME

 

 

Principle: Clotting time is the interval between appearance of blood and appearance of clot .

Apparatus: Capillary tube ( 10cm length) stop watch needle etc.

Principle: 

During coagulation, sol form of the blood is changed to gel form. The elapsed between the moment of escape of blood outside the vessel and the observation of physical change is taken as clotting time. 

Mechanism of coagulation ( Clotting) : 

       The clotting of blood involves following three steps: -

1.  Formation of thromboplastin : When the blood comes in contact with rough surface  or tissue extracts, platelets disintegrates and thromboplastin is generated.
2.  Formation of thrombin: The thromboplastin interacts with plasma prothrombin ( a globulin) and thrombin is formed.
3.  Formation of clot: Thrombin thus formed converts fibrinogen to fibrin ( coagulation)

Although the mechanism of clotting appears to be simple, but there are no direct evidences for above reactions except that of the formation of thrombin. Various factor involved in the clotting independently.

Following are the names of the factors accepted universally:

Factor I	Fibrinogen	Factor VIII	Anti-hemophilic factor
Factor II	Prothrombin	Factor IX	Christmas factor
Factor III	Thromboplastin	Factor X	Stuart's Factor
Factor IV	Calcium	Factor XI	Plasma thromboplastin Antecedent
Factor V	Accelerator globulin	Factor XII	Contact Factor
Factor VI	Absence Factor	Factor XIII	Fibrin stabilizing factor
Factor VII	Stable Factor

Procedure : Wright method

1. The ring finger is sterilized and pricked boldly with needle.
2. As soon as the blood comes out, the stopwatch is started and a capillary tube is filled to three-fourth of its total length.
3. After every 30 sec. a portion of capillary tube ( about 1/10 of the tube) .
4. The time is noted and the difference between the time when blood comes out from the finger and unbroken coagulum seen is the coagulation time.

 Report: The clotting time of my own blood sample was found to be 150 sec.

Discussion:

The time between the moment of escape of blood outside the vessel and the development of fibrin is defined as the "clotting time". The normal clotting time is 4-10 minutes.

The clotting time is shortened by various factors such as warmth, intense surface agitation and tissue factors. Clotting time is prolonged under various conditions a s absence of clotting factor, decrease in temperature, smoothness of surface , dilution of  blood etc.

Hemophillia is the condition caused by the absence of any one of the factor required for clotting of blood. It causes prolongation of clotting time.

Other methods:

Lee and White's method:

About 4cc. of blood is obtained through a vein puncture and 1cc. placed in each of four small test tubes. As soon as blood enters the barrel of syringe, stopwatch is started. The test tubes are placed in water bath at 37 C. The test tubes are titled at every 30 sec. The time when blood does not move on titling is noted down.

Duke's Method: 

The finger is sterilized and I drop approximately 5 mm diameter is placed on special glass slide is held vertical at every 30sec . The time is noted when no change in the shape of the drop is seen. This gives the clotting time.