Clotting time, often referred to as coagulation time, is a key pathology examination utilized to evaluate how effectively blood can clot. This assessment gauges the duration it takes for blood to create a clot following an injury or under controlled laboratory conditions. Clotting time serves as an essential marker of hemostasis, which is the body’s process for preventing and halting bleeding. Irregularities in clotting times may indicate potential issues within the coagulation cascade, including conditions like hemophilia, von Willebrand disease, or liver dysfunction. This article offers a thorough overview of the clotting time test, covering its objectives, methods, clinical relevance, and interpretation.

Principle of Clotting Time

When blood collected through a proper venipuncture is placed in a glass tube, the clotting mechanisms are activated, and a clot subsequently forms. The duration required for the blood to clot in this manner is referred to as whole blood clotting time (CT). Whole blood clotting time is a non-specific and insensitive test. It will remain prolonged only in cases of severe hemophilia or Christmas disease, where factor levels drop to as low as 1 percent. Occasionally, it is utilized as a bedside test to check for the effects of heparin and circulating anticoagulants. The Lee and White method is frequently employed.

What are the Purpose of Clotting Time Test?

The clotting time test serves mainly to:

• Evaluate Hemostasis: Examine how well the blood clotting system is functioning.
• Diagnose Bleeding Disorders: Detect issues such as hemophilia or von Willebrand disease.
• Monitor Anticoagulant Therapy: Verify correct dosages for patients using blood-thinning drugs like heparin.
• Detect Liver Dysfunction: Since the liver generates numerous clotting factors, reduced liver activity can lead to extended clotting times.
• Pre-Surgical Screening: Gauge the risk of bleeding prior to surgical operations.

Methodology for Estimation of Clotting Time

The clotting time test can be performed using several methods, each with varying levels of sensitivity and clinical applicability. The most common techniques include:

1. Lee-White Method

Requirements

• Single-use plastic syringe
• Glass test tubes measuring 75×12 mm (10 mm diameter)
• Water bath maintained at 37°C
• Three stopwatches

Procedure of Lee-White Method

1. Warm three glass test tubes in the water bath at 37°C.
2. Disinfect the venepuncture area with a spirit swab and allow it to dry.
3. Using a single-use plastic syringe, draw 3 ml of blood. As the blood fills the syringe, begin timing with all three stopwatches.
4. Transfer 1 ml of blood into each of the three glass tubes that are already placed in the water bath.
5. Initially, tilt the tubes after 4 minutes and subsequently every 30 seconds to check if the blood has clotted.
6. When clotting occurs in a tube, stop the corresponding stopwatch. Record the time taken for blood to clot in each tube. Calculate the average of the three readings as the final result. This represents the clotting time.

Precautions

• The venepuncture must be performed in a sterile manner, and only samples obtained from a single puncture should be used. Repeated trauma can release more tissue factor, possibly reducing clotting time.
• It is crucial to start the stopwatch immediately as blood enters the syringe.
• The test tubes must have the specified diameter (10 mm) to ensure consistent results.

Reference range

5-11 minutes

2. Capillary Tube Method

A standard incision is made on the patient’s skin, and blood is gathered in a capillary tube. The stopwatch is then initiated. The emergence of a fibrin string is observed by breaking the capillary tube at predetermined intervals. The time is recorded at the initial sighting of the fibrin string.

Requirements:

• 70% ethanol for disinfection.
• A sterile lancet or needle (24G).
• A capillary tube (which contains no anticoagulant).
• A stopwatch.
• Cotton and other materials.

Procedure of Capillary Tube Method

• Carefully sanitize the fingertip using an alcohol swab (cotton soaked in alcohol). Warm the finger prior to puncturing the skin.
• Create an incision with a sterile lancet or needle to a depth of 3mm. As soon as blood becomes visible, start the stopwatch.
• Remove the first droplet of blood and allow the subsequent droplet to fill the capillary tube.
• After 2 minutes, break the capillary tube approximately 1 to 2 cm from the end.
• When a fine fibrin string becomes visible between the broken ends of the capillary tube, stop the stopwatch and record the time.
• Report the time using the specified method.

Normal Range

• Normal clotting time ranges from 2 to 8 minutes.

3. Activated Clotting Time (ACT)

• This method is primarily utilized during surgical procedures or for patients receiving heparin.
• Blood is combined with an activator (such as kaolin) to speed up the clotting process.
• The normal range for ACT is 70 to 120 seconds.

4. Automated Coagulation Analyzers

• Current devices assess clotting time through the use of optical or mechanical sensors.
• These analyzers deliver quick and precise results and are commonly employed in clinical laboratories.

What are Clinical Significance of Clotting Time?

1. Prolonged Clotting Time

• Suggests a possible deficiency or malfunction of clotting factors (e.g., hemophilia A or B).
• May indicate a lack of vitamin K, liver dysfunction, or disseminated intravascular coagulation (DIC).
• Can occur as a result of anticoagulant medications (e.g., heparin or warfarin).

2. Shortened Clotting Time

• Uncommon but may point to hypercoagulable conditions like thrombophilia.
• Can be linked with issues such as deep vein thrombosis (DVT) or pulmonary embolism (PE).

3. Monitoring Anticoagulant Therapy

• Tests of clotting time, especially activated clotting time (ACT), are utilized to oversee heparin treatment during surgeries or dialysis.
• This ensures the maintenance of therapeutic levels while minimizing the risk of excessive bleeding.

Interpretation of Clotting Time Test Results

• Normal Range: This varies based on the method employed (e.g., 2–8 minutes for capillary tubes, 5–15 minutes for the Lee-White method).
• Abnormal Results:
  • Prolonged Clotting Time: This requires further evaluation, which may include specific factor tests (such as Factor VIII or IX) or mixing studies. Clotting time increase in Acute leukemia, Afibrinogenemia, DIC, Dysfibrinogenemia, Dysproteinemias (multiple myeloma), Liver disease, Polycythemia vera etc
  • Shortened Clotting Time: This may lead to evaluations for hypercoagulability, including tests like D-dimer or genetic analyses for thrombophilia. Clotting decrease in Thrombocytosis

Limitations of the Clotting Time Test

• Low Sensitivity: The test might miss mild deficiencies in clotting factors.
• Variable Results: Factors such as temperature, sample preservation, and tube material can influence the results.
• Non-Specific: An extended clotting time does not identify the specific cause of the abnormality.

Advances in Clotting Time Testing

Recent developments have enhanced the precision and effectiveness of clotting time assessments:

• Automated Analyzers: These deliver quick, consistent results while requiring minimal manual effort.
• Point-of-Care Testing (POCT): Tools like the i-STAT system allow for immediate clotting time evaluations in clinical environments.
• Molecular Diagnostics: Genetic testing complements clotting time assessments to identify inherited disorders related to bleeding or clotting.