Coagulation screen


Alternative names, keywords

APTT ratio, activated partial thromboplastin time ratio, INR, international normalized ratio, clotting screen, fibrinogen (Clauss).

Samples required

Trisodium citrate blood (blue cap, 3.5 mL tube) taken with minimal stasis, filled to the line. Smaller tubes are available for paediatric samples.

Samples must be analysed or processed in the laboratory within 4 hours of venepuncture.

Test indications


Reference range


0.8 - 1.2


24.8 - 37.4 s

APTT ratio

0.87 - 1.15

Prothrombin time

11 - 17 s

Fibrinogen (Clauss)

1.8 - 4.5 g/L

Source: locally determined.

Turnaround time

1 working day (2 hours if identified as urgent).


Haematology (Coagulation)