🩸 HAEMOSTASIS SAMPLE COLLECTION AND PROCESSING

Patient Preparation:

• Patients should be advised to avoid strenuous exercise and stress immediately before blood collection.

• Discuss medication history; if necessary, some tests may require a period of discontinuation from anticoagulant prior to the blood draw.

Sample Collection:

• Avoid drawing blood from a drip arm or indwelling catheter to prevent heparin contamination.

• Use a needle gauge between 19-23G to prevent partial activation of haemostasis.

• Minimize tourniquet usage to prevent venous stasis.

• Use 3.2% Sodium Citrate tube.

• Ensure proper filling of tubes - no underfilling or overfilling to maintain a blood to anticoagulant ratio of 9:1. Different tubes will have different sample level indicator marking.

• Immediately invert the tube 4-5 times gently to avoid clotting; avoid vigorous shaking.

• Patients with high haematocrit (>55%) may require adjustment of the anticoagulant/blood volume. Contact the laboratory for citrate volume adjustment.

• Citrate volume adjustment can be calculated using the formula:

C = (1.85 × 103) (100 - Hct)(V)

       C: volume of citrate in mL;

       V: volume of blood in mL (eg in 3 mL tube, volume of blood is 2.7mL)

    Hct: Hematocrit of patient in %

(Ref: Marlar et al; Coagulation Tests and High Hematocrits. Am J Clin Pathol 2006)

Note: Once the volume of anticoagulant and blood is adjusted, the tube should only be used for the intended patient. Please label the tube with patient’s name and IC number.

Sample Processing

• Whole blood samples for coagulation tests should be maintained at ambient temperature of 18-24°C during transport and storage prior to processing.

• Transport sample to laboratory within 2 hours of sample collection.

• If sample cannot reach laboratory within 2 hours, centrifuge and separate the plasma.

• Sample to be transported to referral lab needs to be sent in frozen state. Ideally to transport with dry ice packing (ice packs might not be adequate to ensure sample arrived in optimal condition).

• Platelet poor plasma (PPP) – platelet count <10 x 109/L

• Centrifuge at 1500-2000 g for 10-15 minutes at room temperature

🩸 PRE-ANALYTICAL VARIABLES IN HEMATOLOGY TESTING