Determination of Clotting Time 

Mr. Topesh Patle

AIM: Determination of Clotting Time 

Capillary method

Principle

  • The principle behind the capillary method is that blood, when exposed to air, begins to clot due to the activation of the clotting factors.
  • The time taken for the blood to form a clot is measured.

Requirements

  • Glass capillary tube 

  • Sterile needle or lancet

  • Timer or stopwatch

  • Slides or Petri dish (optional)

  • Alcohol swab

  • Sterile cotton 

Procedure

  1. Clean the area (usually the fingertip or earlobe) with an alcohol swab and allow it to dry.

  2. Prick the skin with a sterile lancet or needle to draw a small amount of blood.

  3. Place the capillary tube at the site of the puncture and allow blood to flow into the tube by capillary action.

  4. Collect a sufficient amount of blood to ensure a reliable test result.

  5. As the blood fills the capillary tube, immediately start the timer.

  6. Observe the blood within the capillary tube for the formation of a clot. You may also place the capillary tube on a slide or petri dish for better visibility.

  7. The time taken from the blood collection until the blood in the capillary tube forms a clot is the clotting time. Typically, this is recorded in seconds.

  8. Apply pressure to the puncture site with sterile cotton to stop any bleeding.

Normal Range

  • Clotting time 2–5 minutes.

Tube method

Principle

  • The tube method is based on the principle that when blood is drawn into a glass tube and exposed to air, it undergoes a series of reactions leading to the formation of a clot.
  • The time required for clot formation is recorded as the clotting time.

Requirements

  • Clean test tube

  • Sterile needle or lancet

  • Timer or stopwatch

  • Sterile cotton

Procedure

  1. Clean the area of blood collection (usually the fingertip or earlobe) using an alcohol swab and allow it to dry.

  2. Prick the site with a sterile lancet or needle to collect a small sample of blood.

  3. Collect the blood directly into a clean, dry glass test tube. The tube should not contain any anticoagulants (such as heparin) because the clotting process must occur naturally.

  4. Immediately start the timer once the blood is drawn into the test tube.

  5. Place the test tube in a warm area, typically at body temperature (37°C), to simulate the physiological conditions under which blood clots in vivo.

  6. Periodically, gently tilt the test tube to check for the formation of the clot. Once the blood starts to clot and does not flow when the tube is tilted, the clotting time is considered complete.

  7. You may observe the clot formation by noting the change in consistency of the blood inside the tube (from liquid to gel-like substance).

  8. Record the exact time from when blood is collected to the moment the clot is fully formed.

  9. Apply pressure on the puncture site to stop any bleeding and ensure hygiene.

Normal Range

  • The normal clotting time – 5 to 15 minutes.

Clinical Significance of Clotting Time

Prolonged Clotting Time

A prolonged clotting time (i.e., the time taken for blood to clot is longer than normal) may be indicative of several underlying conditions, including:

  1. Hemophilia:

    • A genetic disorder where one or more of the clotting factors are deficient or absent, leading to difficulty in forming blood clots.

    • Common in males and can result in spontaneous bleeding or excessive bleeding after minor injuries.

  2. Liver Disease:

    • The liver produces most of the clotting factors. Liver diseases such as cirrhosis, hepatitis, or liver failure may result in reduced production of clotting factors, leading to a prolonged clotting time.

    • This can cause excessive bleeding, even with minor wounds.

  3. Vitamin K Deficiency:

    • Vitamin K is essential for the synthesis of clotting factors (II, VII, IX, X). Deficiency can result from malnutrition, certain medications (e.g., blood thinners), or malabsorption disorders (e.g., celiac disease).

    • This leads to bleeding tendencies and prolonged clotting times.

  4. Disseminated Intravascular Coagulation (DIC):

    • A complex condition where the clotting system is abnormally activated throughout the body, leading to widespread clotting and consumption of clotting factors.

    • Can be caused by infections, trauma, cancer, or obstetric complications like placental abruption.

  5. Blood Thinners (Anticoagulants):

    • Medications such as warfarin or heparin are prescribed to reduce the risk of unwanted blood clots (e.g., in stroke or deep vein thrombosis). These drugs increase clotting time as part of their therapeutic action.

    • Patients on anticoagulants may show prolonged clotting times, and monitoring is required to adjust doses.

  6. Autoimmune Disorders (e.g., Lupus):

    • Certain autoimmune diseases can affect the clotting system, leading to prolonged clotting times. Antibodies in conditions like lupus can target clotting factors or inhibit normal clot formation.

  7. Renal Disease:

    • Kidney failure can result in an imbalance of clotting factors and platelets, affecting the blood’s ability to clot and resulting in prolonged clotting times.

Shortened Clotting Time

  1. Hypercoagulable States:

    • Conditions where there is an increased risk of abnormal blood clotting, such as:

      • Pregnancy: Increased clotting factors during pregnancy, especially in the later stages.

      • Cancer: Some cancers (e.g., pancreatic, ovarian) can cause hypercoagulability, leading to an increased risk of thrombosis (blood clots).

      • Oral Contraceptives/Hormone Therapy: Estrogen-based medications can increase clotting factor levels.

      • Genetic Disorders: Conditions like Factor V Leiden mutation or Prothrombin gene mutation that predispose individuals to blood clots.

  2. Platelet Disorders (e.g., Thrombocytosis):

    • In certain conditions like essential thrombocythemia or polycythemia vera, there is an increase in the number of platelets, which can result in a higher risk of clot formation.

    • While the clotting time itself may be shortened, the abnormal clotting can lead to thrombosis (clot formation within the blood vessels).

  3. Dehydration:

    • Severe dehydration can lead to thickening of the blood (hemoconcentration), which might accelerate clotting in some cases.

  4. Trauma or Surgery:

    • Following major trauma or surgery, the body may increase the production of clotting factors to prevent excessive bleeding. This can lead to a shortened clotting time, though excessive clotting could cause complications like deep vein thrombosis (DVT).

  5. Smoking:

    • Smoking is associated with an increased risk of clotting due to changes in blood viscosity and platelet function.

Significance of Monitoring Clotting Time

Monitoring clotting time is essential in clinical settings for:

  • Preoperative Assessments: To ensure patients have normal clotting ability before surgery.

  • Emergency Medicine: To assess bleeding risks in trauma patients.

  • Anticoagulant Therapy: To monitor the effects of blood thinners and prevent over- or under-anticoagulation.

  • Chronic Disease Monitoring: To monitor and manage clotting risks in patients with chronic conditions like liver disease, kidney failure, or cancer.