Activated Partial Thromboplastin Time (APTT)

1. Add 0.1ml of platelet substitute, diluted 1:2 with saline, to a 75x10mm tube.
2. Add 0.1ml plasma and warm for 1 min at 37°C.
3. Add 0.1ml kaolin to the tube. Start the clock and tilt the tube 3 times. The incubation time varies from 5-10 min, depending on the reagents used.
4. Add 0.1ml calcium chloride. Start the clock and observe for clot formation by tilting gently at regular intervals.

Compare with a normal or control plasma sample measured at the same time.
Normal APTT is between 38 and 45s, depending on the reagent used.