The following points highlight the top two methods for clotting time. The methods are: 1. Capillary Tube Method 2. Lee and White Method.
1. Capillary Tube Method:
Procedure:
i. Clean the tip of a finger with spirit.
ii. Puncture it upto 3 mm deep with a disposable needle.
iii. Start the stopwatch.
iv. Fill two capillary tube with free flowing blood form the puncture after wiping the first drip of blood.
v. Keep these tubes at body temperature.
vi. After 2 minutes, start breaking the capillary tube at 1 cm distance to see whether a thin fibrin stand is formed between the two broken ends.
vii. Stop the watch and calculate the time from average of the tow capillary tubes.
Disadvantages:
(i) Method is insensitive.
(ii) Method is unreliable.
Advantages:
It can be performed when venous blood cannot be obtained.
Normal clotting time is 1-5 minutes.
2. Lee and White Method:
Procedure:
i. After cleaning the forearm, make a venepuncture an draw 3 ml of blood in a silicon-sided glass or plast syringe.
ii. Start the stopwatch.
iii. Transfer 1 ml of blood each into 3 glass tubes which at kept 37° C in a water bath (Fig. 31.1)
iv. After 3 minutes tilt the tubes one by one every 30 second.
v. The clotting time is taken when the tubes can be title without spilling of their contents.
vi. Calculate the clotting time by average of 3 tube.
Advantages:
(i) More accurate and standard method.
(ii) Test can be run with control.
Disadvantages:
(i) It is also a rough method.
(ii) There can be contamination of syringe or tube.
Normal clotting time is 5-10 minutes.
Disadvantages:
(i) The temperature should be maintained because higher temperature accelerates clotting.
(ii) The diameter of the glass tubes should be uniform because clotting is accelerated in narrow tubes.
(iii) Vigorous agitation of the tubes should be avoided as it shortens the clotting time.
Clinical Application of Clotting Time:
Clotting time is prolonged in following conditions:
(i) Sever deficiency of coagulation factors.
(ii) Afibrinogenaemia.
(iii) Administration of heparin.
(iv) Disseminated intravascular coagulation (DIC).
(v) Administration of drugs such as anticoagulants.