Clotting Time (C T)
Sample
- Clotting Time is done on a fresh blood sample, and the patient needed to be in the lab.
Indications
- Clotting Time is advised to find bleeding disorder, most likely due to clotting factors deficiency.
- To Diagnose hemophilia.
Precautions
- It does not diagnose mild coagulation disorders.
- Blood should be taken in the least traumatic manner.
- The premature activation of the clotting process must be avoided to ensure an accurate result.
- Avoid hemolysis of the sample.
- It is important to get the history of the patient:
- Note physical appearance, site, the severity of the disease, and frequency of the bleeding episodes.
- Get an accurate history of the drugs.
- A patient and the family history in detail needed.
- Also, consider other contributing or underlying diseases.
Pathophysiology
- For clot formation, prothrombin is converted into thrombin.
- Thrombin converts soluble fibrinogen into insoluble fibrin.
- For this process, clotting factors are needed, along with calcium.
- Also assisted by the factors produced by platelets and damaged tissue.
- So clotting time is the time needed for the generation of thrombin from the complex system of clotting.
- When there is any deficiency in these factors, it will lead to prolonged clotting time.
- It is rarely used because of the variation; instead, the clotting factors are more accurate.
Procedure
- Two methods can estimate clotting time:
- Capillary method.
- Prick the finger with the lancet.
- Hold the capillary over the blood, and the capillary will fill automatically.
- Now, after regular intervals, break the capillary.
- When a clot starts forming, that is the endpoint and clotting time.
- Test tube method.
- Perform this test at 37 ° C.
- For the tube method, take 4 ml of blood and start the time.
- Note the time when there is the first appearance of the clot formation.
- This test can be done in multiple tubes to be more accurate.
- Capillary method.
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- Lee and white method:
- Two siliconized tubes with a 10 cms external bore are taken.
- These tubes are prewarmed at 37 °C in a water bath.
- Take the blood mostly from the antecubital vein.
- 2 to 2.5 mL of the blood is taken, and 1 mL of the blood in each test tubes.
- Start two stopwatches as you see the blood in the syringe.
- Keep the blood in the water-bath and check for clotting by tilting each tube at intervals of 30 to 60 seconds.
- Tilt the tube to greater than 90 degrees.
- Stop the stopwatch as you see the clot in the tube.
- Clotting time is expressed as the mean of the two stopwatches.
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Disadvantages of clotting time:
- This test is insensitive, so it lost its value.
- There are many variables in the technique of performing the test.
- This fails to detect the moderate deficiency of coagulation factors.
- This test is only prolonged in severe deficiency.
- Normal clotting time is despite prolonged bleeding time seen in thrombocytopenia.
- This may be normal in patients taking anticoagulant therapy.
- This is usually normal when the intrinsic and common pathways are present in an amount not exceeding 1% of the normal plasma level.
- Because of all the above reasons, this test has lost its significance.
- Lee and white method:
Normal
- The expected range is 4 to 10 minutes.
- The glass tube method clotting time is 5 to 15 minutes.
- Siliconized tube’s clotting time is 19 to 60 minutes (reference: Interpretation of diagnostic test by Jacques Wallach M.D.)
Causes of prolonged clotting time are:
- Coagulation factors deficiencies which may be:
- Congenital.
- Acquired.
- Severe deficiency of any known plasma clotting factors except XIII (fibrin-stabilizing factor) and VII.
- Drugs like heparin and thrombin inhibitor.
- Marked hyperheparinemia.
- Afibrinogenemia.
Coagulation time normal seen in:
- Thrombocytopenia.
- Deficiency factor VII.
- Mild coagulation defects due to any reason.
- Von Willebrand syndrome.
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