PROTOCOL

1. Dispense 2ml of freshly drawn whole blood into each of three siliceous earth vacutainers (Becton Dickinson) and commence timing immediately. Jugular venupuncture is recommended to minimise the delay between sampling and commencing timing.
1. Gently invert each tube five times.
1. Tilt each tube gently at 10 second intervals and observe the blood as it spreads along the length of the tube.
1. The ACT is the mean time taken to the appearance of the first unmistakable clot in each of the three tubes (this precedes the formation of a solid clot involving the whole sample).

With the test performed at room temperature, the normal range for the ACT is 83 to 129 seconds with a mean time of 103 seconds. This reference range applies where blood is collected by venupuncture and timing commenced immediately that blood enters the tube. Where a syringe and needle are used and blood is transferred to the siliceous earth vacutainer tubes, ACT's may be correspondingly shorter. An ACT of >125 seconds should be considered abnormal.

In normal dogs, the time between the end point and the formation of a total clot is short (seconds). In dogs with a coagulopathy this time is often increased.

The ACT test is not as sensitive as the Activated Partial Thromboplastin Time (APTT) test in detecting defects in the intrinsic clotting pathway. Sensitivity can be improved by performing the ACT test in pre-warmed siliceous earth vacutainers at 37° C. At this temperature the normal range for the ACT is 64-95 seconds with a mean of 79 seconds. An ACT of >95 seconds should be considered abnormal.

After completing the ACT test, the clots should retract to 50% of their original volume. The Clot Retraction Test is a crude measure of platelet function.

REFERENCES

Littlewood, J.D (1992). Differential diagnosis of haemorrhagic disorders in dogs. In Practice. 14(4) p172 - 180.

Middleton, D.J and Watson, A.D (1978). Activated coagulation times of whole blood in normal dogs and dogs with coagulopathies. J.Small.Anim.Pract. 19 p 417 - 422.