EXPERIMENT NO. 04
“TO DETERMINE THE CLOTTING TIME OF A SUBJECT”
Theory:
Clotting time: It is the time interval in between onset of bleeding and appearance of jelly like
semisolid mass i.e. blood clot.
The basis for the test is that whole blood will form a solid clot when exposed to a foreign surface
such as glass tube.
It is a rough measure of all intrinsic clotting factors in the absence of tissue factors. Variations are
wide and the test sensitivity is limited.
Significance of test: Clotting time was used as a screening test to measure all stages in the
intrinsic coagulation system and to monitor heparin therapy.
Procedure:
Clotting time can be measured by three methods: Capillary tube method, Drop method and lee
white method.
(i).
Capillary tube method:
 Requirements:
Pricking needle or lance, stop watch, dry glass capillary tube (narrow diameter 1 to 2 mm,
minimum 10cm long), cotton swab of absorbent cotton, alcoholic swab.
 Method:
1.
2.
3.
4.
Apply alcoholic cotton swab on fingertip. Allow it to dry naturally.
Prick the finger, immediately stop watch is started.
Dip one end of the capillary tube in the blood drop gently without pressure.
Allow to fill the capillary tube with blood by lowering the end of fitted capillary. (Do not suck the
blood) around 3/4th of its length undipped.
5. After every 30 seconds, using stop watch, break a small piece of capillary.
6. Repeat breaking at regular time intervals, till fibrin thread appears at the broken end of capillary
tube. Do not pull away the cut pieces ling apart and bristly.
7. Record time intervals between pricking finger and first appearance of fibrin thread at the broken
ends of capillary tube. That is clotting time of blood.
Normal clotting time: 2 to 9 minutes.
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(ii).
Drop method:
 Requirements:
Glass slide and needle
 Method:
1. Place a drop of blood from the skin puncture on a dry glass slide.
2. Start the stop watch and note the time.
3. Draw a pin through the drop every 30 secs and note the time when fibrin thread adhere to the
pin and move with it out to the blood drop.
4. The time interval between placing the blood drop on the slide and the formation of fibrin threads
is taken as the clotting time.
Normal Range: 2-4 minutes
(iii). Tube method (Lee-White method):
 Requirements:
Water bath, 370 C, test tube, stop watch, syringes, fresh whole blood 4 ml.
 Method:
1. Label 3 glass test tubes with patient name and number them, 1, 2, and 3.
2. Perform a clean, Untraumatic venipucture using a 20-gauge needle and drawn 4 ml of blood.
3. Remove the needle from the syringe, and fill each of the three tubes with 1 ml blood.

The last 1 ml of blood may be discarded.

Start the stop watch as soon as the blood enters the syringe.
4. Place the three test tubes in a 370 C water bath.
5. At exactly 3 min, remove the first tube from water bath and tilt gently to a 450 angle to see
whether the blood has clotted.
6. If blood not clotted f\return it to the water bath and examine it at 30 second intervals.
7. After the blood in the first tube has clotted, examine the second tube immediately.
8. Then examine the 3rd one.
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9. Record the time it took the blood in the 3rd test tube to clot.
 Normal Range: 5-12 minutes
Observation:
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Result:
The clotting time of a subject is ……………...........................................
Abnormal findings:
Clotting time is prolonged in hemophilia. Liver diseases, Afibrinogenemia, Christmas disease,
Vitamin K deficiency.
Sources of Error:
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VIVA related questions:
1. State two pathological conditions when clotting time is prolonged.
2. State two physiological conditions when clotting time is reduced.
3. What is hemophilia? What happens to bleeding and clotting time in this disease?
4. Why bleeding time is smaller than clotting time? Give the reason.
5. What I thrombocytopenia?
6. Define hemostasis. What are the factors that affect hemostasis?
7. Schematically represents the intrinsic and extrinsic pathway of blood clotting.
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WORK PAGE
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