Clotting time – when to test, what it depends on, analysis of the results

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The clotting time is a test that reflects the activation time of the clotting system under artificial conditions. It mainly depends on the plasma function of coagulation factors I, II, V, VIII, IX, X, XI and XII. We test the clotting time in the event of suspicion of its disorders.

What is clotting time?

The clotting time is the time that elapses from the moment the material is collected for testing until it finally solidifies under artificial conditions. In this way, some elements of the blood coagulation system are assessed, especially the final stage of the clotting process, i.e. the transformation of artificial fibrinogen into insoluble, blood-sticking fibrin. The method is most often used to test blood clotting Lee-White’a. It allows the efficiency of the entire coagulation system to be assessed, with particular emphasis on activity Hageman factor (it is plasma blood coagulation factor XII). Blood clotting testing is a complicated process that requires the following elements to work together:

1. activation, adherence and aggregation of platelets (they accumulate at the site of vessel damage and form a plug that inhibits the outflow of blood),
2. spasm of blood vessels due to their damage,
3. activation of blood plasma proteins that play a vital role behind clotting.

Proper cooperation of the mentioned elements leads to the closure of the damaged vessel by the formation of a clot. Coagulation testing is currently very rarely performed because this method is not standardized and there is a low reproducibility of the results and new, better methods of determination. It should be mentioned, however, that thanks to the blood clotting test, certain conclusions can be drawn about the level and function of some clotting factors.

When do we do a blood clotting test?

Although currently blood clotting is rarely performed (replaced with more detailed measurements, e.g. platelet count, PTT, APTT), its prolongation is observed in the case of abnormal levels or activity of clotting factors, especially those taking part in the so-called by the intrinsic coagulation pathway. The most common indications for a blood clotting test are:

1. prolonged and intense bleeding from the nose or gums (the most characteristic symptom of a bleeding disorder). Haemorrhagic diathesis is associated with reduced production or activity of proteins that are involved in the blood clotting process. These disorders may be acquired or congenital (e.g. haemophilia),
2. formation of bruises and hematomas after impact,
3. diseases that reduce the production of coagulation factors (they can also cause plasma hemorrhagic diathesis). Coagulation factors in the body are produced by the liver, therefore liver diseases, such as liver failure, lead to a prolonged clotting time. A similar situation occurs when there is a vitamin K deficiency,
4. control of treatment with heparin (it is a blood thinner).

Clotting time – study

1. Material for the coagulation test: citrate plasma.
2. Preparation for the test: on an empty stomach (at least 8 hours). In any case, you should inform your doctor about the medications you are taking (even dietary supplements) and about current diseases. This can be crucial in interpreting test results.
3. Procedure: one-time collection of blood from a vein in the arm with a sterile needle and placing the blood in a test tube. The collected material is sent for further laboratory analysis. After the examination, you can return to the previous activities.
4. Time of waiting for the result: 1 day.
5. Norms: in healthy people, the clotting time should be: 7-9 minutes at 37 ° C and 6-12 minutes at room temperature. It should be taken into account that there are many methods of conducting the test, so reading the result is subjective. The reference values ​​may differ depending on the laboratory where the test has been carried out.

Comments: A prolongation of the clotting time is observed in the presence of a significant deficiency of plasma coagulation factors (less than 5% of the normal value).

Also read: When blood clots too much

Elements influencing blood clotting time

The following items can affect the timing of blood clotting:

1. tube size,
2. model of the test tube (glass, silicone),
3. glass model from which the test tubes are made.

How should the results of blood clotting tests be analyzed?

It is difficult to interpret the result of a blood clotting test unambiguously as there are many factors that influence the result. A normal blood clotting result does not mean that homeostasis has not been disturbed.

Blood clotting is prolonged in the following situations:

1. during treatment with heparin: it inhibits the coagulation process, and while taking it, haemostasis should be controlled,
2. haemophilia: otherwise hemorrhagic diathesis based on deficiency of clotting factors VIII, IX, or XI. They should be constantly supplemented, especially before procedures or operations (may lead to hemorrhage),
3. deficiency of clotting elements II, V, VIII, IX, X, XI, XII: their absence leads to the formation of a hemorrhagic diathesis,
4. anticoagulants: antiphospholipid antibodies that are revealed in the antiphospholipid syndrome and systemic lupus,
5. impairment of the plasma coagulation phase (difficult activation of subsequent clotting factors with the final formation of insoluble fibrin),

Blood clotting results may be false if taken during menstruation or pregnancy.

Too short clotting time may be caused, for example, by hypercoagulability, thrombophilia, thrombosis, or in pregnant and postpartum women. Increased factor VII activity is also important.

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