Bleeding time

It involves cutting the underside of the subject's forearm, in an area where there is no hair or visible veins. The cut is of a standardised width and depth, and is done quickly by an automatic device.

A blood pressure cuff is used above the wound, to maintain venous pressure at 40 mmHg.

The time it takes for bleeding to stop (as thus the time it takes for a platelet plug[?] to form) is measured. Cessation of bleeding can be determined by blotting away the blood constantly until the site looks 'glassy'.

Bleeding time is affected by platelet function, and not by other coagulation factors so in haemophilia it is normal.

Aspirin and other drugs can prolong bleeding time significantly.

Normal values fall between 2 - 8 minutes.