Assessment of clotting, tests and interpretation

Platelet count

            Pathway tested: Primary haemostasis

            Method: Automatic counter inaccurate

                           Manual count better

                           Assessment of blood smear can indicate if platelet levels are                                       adequate. 11-25 platelets/oil immersion field is equivalent to an approximate count of >165x10⁹/l

            Normal values:  Dog 150-400x10⁹/l

                                                Cat 150-400 x10⁹/l

            Abnormal values:          low values (thrombocytopenia) may be due to excessive consumption eg bleeding, immune-mediated destruction, sequestration, or reduced production eg bone marrow disease

                                                High values may be due to physiological causes eg splenic contraction, rebound thrombocytosis post-thrombocytopenia, reactive thrombocytosis in non-specific inflammatory conditions and primary thrombocytosis such as platelet leukaemia.

Buccal mucosal bleeding time

            Pathway tested: Primary haemostasis (platelet function)

            Method: The upper lip is tied back and a shallow incision made in the non-vascular mucosa with a spring0loaded cutting device such as a Simplate or Surgicutt). Filter or blotting paper is used to absorb blood without touching the wound and disturbing the forming clot. The time taken for bleeding to stop is measured.

            Normal values: Dog 1.7 to 4.2 minutes

                                                Cat   1.0 to 2.4 minutes

            Abnormal values:          Elevated bleeding times are seen in problems of platelet number eg immune-mediated thrombocytopenia, and problems of platelet function such as von Willebrand’s disease.

Clot retraction

            Pathway tested: Primary haemostasis (platelet function)

            Method: Add 1ml of whole blood to a glass tube containing 1ml of 0.9% saline and allow to clot. Examine the tube hourly for signs of clot retraction.

            Normal values: The clot should reduce to approximately 50% of its original volume within 2 hours.

            Abnormal values: Failure of clot retraction implies severe thrombocyte dysfunction.

vWF antigen

            Pathway tested: Primary haemostastis (platelet function)

            Method: Collect blood into trisodium citrate, separate immediately and send to lab. Discuss sample and shipping requirements with lab first.

            Normal values: see individual labs

            Abnormal values: vWF is decreased in von Willebrands disease. It may be increased in physiological conditions such as exercise and parturition, and pathological conditions such as liver disease and azotaemia.

Activated clotting time

            Pathway tested: Secondary haemostasis (intrinsic and common pathways)

            Method: Prewarm a tube containing diatomaceous earth to 37C. Discard fist 0.5ml of blood. Draw up a further 2ml and add to tube. Mix gently and incubate at 37C. Tilt every 10 seconds to examine for the first signs of coagulation.

            Normal values: Dog 60 to 110 seconds, Cat 50 to 75 seconds

            Abnormal values: Increased ACT implies a severe abnormality of the intrinsic and/or common pathways, but will also be increased in severe thrombocytopenia and hypofibrinogenaemia.

Whole blood clotting time

            Pathway tested: Secondary haemostasis (intrinsic and common pathways)

            Method: Discard the first 0,5 ml of blood, then draw 4ml of blood and place 2ml into each of 2 glass tubes. Record the time until coagulation has occurred, gently tilting the tube to 90 degrees every 30 seconds to observe clotting.

            Normal values: Dog and cat 6 to 7 minutes

            Abnormal values: Increased WBCT implies a severe abnormality of the intrinsic and/or common pathways, but will also be increased in severe thrombocytopenia and hypofibrinogenaemia.

Prothrombin time

            Pathway tested: Secondary haemostasis (extrinsic and common pathways)

            Method: Take blood into a sodium citrate to the exact fill level. Discuss shipping requirements with lab.

            Normal values: See individual labs

            Abnormal values: Prolongation of PT occurs with acquired vitamin K deficiency, liver disease, specific inherited factor deficiencies and DIC

Activated partial thromboplastin time

            Pathway tested: Secondary haemostasis (intrinsic and common pathways)

            Method: Take blood into a sodium citrate to the exact fill level. Discuss shipping requirements with lab.

            Normal values: See individual labs

            Abnormal values: Prolongation of APTT occurs in specific factor deficiencies eg Haemophilia A.

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Last modified: December 08, 2003