Urea

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 from alpha granules.
• Venous blood should be collected into coagulation tubes containing Sodium Citrate 3.2%, 0.105M.
• 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 to clotting times. A target blood to anticoagulant ratio of 9:1 is optimal.  Under- or over- filled specimens will not be processed this can adversely affect results.  
• Any warfarin treatment should be mentioned on the request form.
• Sample rejection Criteria: Clotted sample, grossly hemolyzed sample, underfilled/overfilled specimen, unlabeled sample, mismatched patient ID, aged samples, wrong sample tube (citrate tube only).

Transportation and Storage

• PT/INR specimens should be transported to the laboratory at room temperature.
• Coagulation specimens should ideally be analysed within 4 hours of collection. Where this is not possible, centrifuge specimens at room temperature (RT) @ 1500RCF 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.
• Effect of freezing on Coagulation Specimens.
• A 14days in-house study on the effect of freezing, on coagulation specimens at -20oC, showed that there was negligible and clinically non-significant effect of freezing on coagulation specimen results. Therefore frozen citrated coagulation samples are stable for 14 days at -20oC, post centrifugation. This study is available in-house for reference.