Blood Clotting and Hemostasis

Bleeding and Hemostasis

• Bleeding is the loss of blood from damaged or injured blood vessels.
• Hemostasis is the process of preventing blood loss through the injured vessel, involving a series of events leading to clot formation and prevention of further blood loss.
• Steps of blood clot formation:
  • Vasoconstriction (contraction of injured blood vessels)
  • Platelet plug formation
  • Formation of a blood clot

Bleeding Time (BT)

• Bleeding time is a test of hemostasis, indicating how well platelets interact with blood vessel walls to form blood clots.
• Measured from the onset of the wound until the bleeding stops.
• Purpose: detecting platelet defects and evaluating their function.
• Normal value: 1-5 minutes
• Prolonged bleeding time can occur in:
  • Hemophilia
  • Thrombocytopenia
  • Platelet functional disorders
  • Aspirin use
  • Vessel wall defects

Experimental Methods of Bleeding Time

• Two main methods:
  • Duke's method
  • Ivy's method

Duke's Method

• Materials required:
  • Disposable lancet
  • Clean filter papers
  • Stop watch
  • 70% alcohol
  • Cotton
• Procedure:
  • Clean the tip of a finger with alcohol
  • Puncture the finger using a sterile lancet
  • Start the stopwatch
  • Blot the blood with filter paper every 30 seconds
  • Record the time when the filter paper no longer shows signs of blood
• Normal range: 2-5 minutes

Ivy's Method

• Materials required:
  • Disposable lancet
  • Filter paper
  • Sphygmomanometer
  • Stop watch
  • 70% alcohol
• Procedure:
  • Clean the front surface of the forearm with 70% alcohol
  • Place a sphygmomanometer cuff around the patient's upper arm and raise the pressure to 40 mmHg
  • Make one, two, or three punctures in the front surface of the forearm
  • Start the stopwatch
  • Remove the drops of blood with filter paper every 30 seconds
  • Record the time when the bleeding stops
• Normal range: 1.5-4 minutes

Clotting Time

• Clotting time is the time required for blood to clot under certain conditions.
• When the blood vessels rupture, the blood loses its fluidity and sets into a semisolid mass called the "clot".
• Normal clotting time range: 3-10 minutes
• Clotting time prolonged in:
  • Hemophilia
  • Vitamin K deficiency

Experimental Methods of Clotting Time

• Two main methods:
  • Capillary tube method (Wright's method)
  • Slide method

Capillary Tube Method (Wright's Method)

• Materials required:
  • Disposable lancet or needle
  • Stop watch
  • Capillary tube (non-heparinized)
  • Cotton
  • 70% alcohol
• Procedure:
  • Clean the finger with alcohol
  • Puncture the finger by lancet and record the time immediately
  • Squeeze the finger to obtain a large drop of blood and fill the capillary tube with blood
  • Record the time when the clot forms