Haemostasis: diagnostic techniques

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Adequate haemostasis depends on normal structure and function of the blood vascular system, the number and functional integrity of platelets, and an adequate coagulation system, including stability of the fibrin clot. This chapter looks at indications for haemostasis testing; sample collection and handling; global testing; basic haemostasis profile; further and specific tests.

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22.2 Influence of haematocrit (Hct) on the ratio of blood to anticoagulant in citrated blood. In a sample with normal haematocrit (50%), the ratio between plasma and citrate is approximately 4.5:1 (left-hand column), whereas the ratio is approximately 8:1 in a sample with a haematocrit of 10% (middle column). Deliberate underfilling of the tube to approximately 60% results in an adequate ratio (right-hand column).
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22.3 Schematic TEG/ROTEM traces indicating: the commonly reported variables: reaction time (R)/clotting time (CT), clot formation time (K/CFT), alpha angle (α), maximum amplitude (MA)/maximum clot firmness (MCF), and lysis (Ly)/clot lysis (CL), and different characteristic patterns: A normal, B hypercoagulability, C hypocoagulability (e.g. thrombocytopenia/thrombocytopathia), D primary hyperfibrinolysis.
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22.4 Visual platelet count. The contents of a capillary tube containing EDTA blood are emptied into a sample tube containing a haemolytic and dilution medium (Thrombo Plus system). The figure also demonstrates the sample applicator stick (within the tube), which is attached to the lid of the sample tube and can be used to load the haemocytometer by capillary action. In the counting chamber, platelets are detected as small dots with a light centre and must be differentiated from the larger white blood cells (in the middle of the right-hand side, two white blood cells can be seen; cell shadows in the background represent lysed red blood cells).
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22.5 Capillary bleeding time. A non-anaesthetized dog is held in lateral recumbency and a hyperaemic agent is applied to the shaved lateral side of a front toe. A blood lancet is used to make two punctures close to the edge of the keratinized skin of the footpad. The bleeding time is detected by carefully dabbing the blood from these two sites with a swab every 15 seconds until the bleeding stops.
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22.6 Technique for the measurement of buccal mucosal bleeding time (BMBT) in the dog.
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22.7 Classical schedule of the haemostasis system, indicating areas examined by the three group tests: prothrombin time (PT), activated partial thromboplastin time (aPTT) and thrombin time. Ca, calcium ions; F, (coagulation) factor; HMWK, high molecular weight kininogen; PL, phospholipid.
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22.9 Schematic diagram of the cross-sectional view of the functional unit of the platelet function analyser PFA-100.
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