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Clotting Time Blood Test

Last updated June 19, 2019

Approved by: Maulik P. Purohit MD, MPH

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The Clotting Time Blood Test helps determine the time it takes for a sample of blood to form a blood clot while in a glass test tube of standard size.

What are other Names for this Test? (Equivalent Terms)

  • Coagulation Time Blood Test
  • Lee-White Clotting Time Blood Test

What is Clotting Time Blood Test? (Background Information)

  • Clotting is the process by which components in blood form a blood clot. These components include platelets and various blood proteins
  • A blood clot is a mass formed within a blood vessel to stop bleeding by blockading the wound, preventing the escape of blood from the blood vessel. Formation of a blood clot is a multistep process that is tightly regulated
  • Blood clot formation normally starts with injury to a blood vessel, which causes it to constrict. Called the vascular phase, this is the first reaction of a blood vessel to damage. It reduces the flow of blood to the site of injury, minimizing blood loss
  • Next, the circulating platelets clump along the site of blood vessel injury. The platelets form a foundation for a blood clot and release chemicals that stimulate clotting
  • The coagulation phase then causes a blood clot to form. Clotting occurs when an enzyme called thrombin converts a soluble protein, fibrinogen, into its insoluble form, fibrin. Fibrin proteins make up the bulk of a blood clot
  • Thrombin is activated by the merging of two pathways, the intrinsic and extrinsic pathways, into the common pathway. These are initiated by different parts of the body after blood vessel damage:
    • The intrinsic pathway begins in blood with the activation of circulating proteins;
    • The extrinsic pathway begins in the blood vessel with the release of protein factors by damaged cells lining the vessel
  • The extrinsic pathway is the first to activate. The intrinsic pathway then reinforces the extrinsic pathway and provides longer-lasting clotting effects
  • Coagulation factors are central to the action of these pathways. Each factor activates the next in a stepwise fashion. Once a coagulation factor is activated, it remains active. Thus, with each step in the pathway, more and more factors are activated. This results in a cascade of events similar to the snowball effect
  • A counter pathway ensures that the size of the growing blood clot stays in check. Problems with this regulatory pathway may lead to a dangerous condition where a blood clot forms within blood vessels (thrombosis)
  • The Clotting Time Blood Test helps determine the time it takes for a sample of blood to form a blood clot while in a glass test tube of standard size. It was once regularly used to diagnose clotting disorders; but presently, the test is rarely used

What are the Clinical Indications for performing the Clotting Time Blood Test?

Following are the clinical indications for performing the Clotting Time Blood Test:

  • Measuring coagulation ability when more sophisticated methods are unavailable
  • Family history of blood clotting disorders
  • Monitoring hemostatic therapy
  • Excessive bleeding
  • Bruising

How is the Specimen Collected for Clotting Time Blood Test?

Following is the specimen collection process for Clotting Time Blood Test:

Sample required: Blood

Process of obtaining blood sample in adults:

  • A band is wrapped around the arm, 3-4 inches above the collection site (superficial vein that lies within the elbow pit)
  • The site is cleaned with 70% alcohol in an outward spiral, away from the zone of needle insertion
  • The needle cap is removed and is held in line with the vein, pulling the skin tight
  • With a small and quick thrust, the vein is penetrated using the needle
  • The required amount of blood sample is collected by pulling the plunger of the syringe out slowly
  • The wrap band is removed, gauze is placed on the collection site, and the needle is removed
  • The blood is immediately transferred into the blood container, which has the appropriate preservative/clot activator/anti-coagulant
  • The syringe and the needle are disposed into the appropriate “sharp container” for safe and hygienic disposal

Preparation required: No special preparation is needed prior to the test.

What is the Significance of the Clotting Time Blood Test Result?

The significance of the Clotting Time Blood Test result is explained.

  • A high value for the test may indicate:
    • Hemophilia disorders
    • Congenital deficiencies in clotting factors
  • A low value for the test may indicate:
    • Disseminated intravascular coagulation (DIC)
    • Thrombotic predisposition

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

  • The Clotting Time Blood Test is not often performed in modern clinical practice because of inconsistencies and other inaccuracies. Presently, more sophisticated and standardized methods are used instead

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider of the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

The following DoveMed website links are useful resources for additional information:



Please visit our Laboratory Procedures Center for more physician-approved health information:


References and Information Sources used for the Article:

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Jan. 17, 2016
Last updated: June 19, 2019