SAMPLE REQUIREMENTS FOR COAGULATION TESTS

PROCEDURE

Sample Requirements and Collection

• Patients should be relaxed pre-venepuncture. Excessive stress and exercise will increase FVIII, vWF antigen and fibrinolysis. Venous occlusion should be avoided.
• Difficult venepuncture with trauma may lead to platelet activation with release of PF4 fromalpha granules.
• Venous blood should be collected into coagulation tubes containing Sodium Citrate 3.2%, 0.105M, 3ml.
• Specimens must be mixed immediately post venepuncture to avoid clot activation, by GENTLY inverting the tubes 5 to 10 times.
• The ratio of whole blood to anticoagulant is crucial. Under-filled specimens will not be processed as over- or under-filled tubes can adversely affect results.
• Any warfarin treatment should be mentioned on the request form.

Transportation and Storage

• PT/INR specimens should ideally be analysed within 12 hours of collection and transported to the laboratory at room temperature.
• APTT and Fibrinogen should ideally be analysed within 4 hours of collection. Where this is not possible please centrifuge at room temperature (RT) @3000rpm (1500g) for at least 15 minutes, and then carefully remove the plasma from the cells, transfer to a fresh plastic plain tube and freeze at -20oC.
• Non-frozen coagulation specimens should be transported at RT ASAP to avoid deterioration of labile factors V and VIII.
• Collection of blood through intravenous lines that have been previously flushed with heparin should be avoided. In the event blood is drawn from an indwelling catheter, the line should be flushed with 5ml of saline, and the first 5ml of blood or 6 times the line volume be drawn off and discarded before coagulation tube is filled.

Plasma Sample Stability (CLSI H21-A5)

• PT 24 hours @ RT or 2 weeks @ -20oC
• APTT 4 hours @ RT or 2 weeks @ -20oC & 12 Months @ -70oC
• Fibrinogen - 4 hours @ RT `

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