Welcome to the Exeter Clinical Laboratory International website
NHS logo

Prothrombin Time (PT)

Blood Sciences Test Haematology


Sodium citrate tube (blue top)

For Neonates we can prepare half volume paediatric tubes, which will require 0.65 mL blood (filled to the black line). Please contact the Coagulation Section on extension 2916 before 1600 weekdays if you require these tubes.

Special Instructions

The tube must be filled correctly (filled to line on tube).

Samples should be received in the laboratory on the same day.

Factors affecting results

Haemolysed or clotted samples cannot be tested. To avoid haemolysis and clotted samples mix tube gently by inversion, do not shake.

Patients on anticoagulants will have abnormal results

Reference Ranges


  • PT: 11-14 sec
  • From:¬†Williams M, Chalmers E,Gibson B ¬†British Journal of Haematology 2002 119: 295 – 309,Andrew M et al Blood 1992 80: 1998 – 2005


In house

The prothrombin time is performed as part of the Coagulation Screen (Diagnostic).

STAT availability


Turnaround times

1 hr – STAT samples

4 hr – routine samples

Clinical Advice

Clinical advice is available from the Haematology Medical team (contact RD&E switchboard on 01392 411611)

Specimen Labelling Procedure
University of Exeter logo
UKAS Medical logo


Royal Devon University Healthcare logo