Prekallikrein (Fletcher) Screening
Specimen requirements:
Fresh whole blood collected in sodium citrate at a 9:1 ratio of blood to anticoagulant
Principle:
The prolonged aPTT is repeated using 10 minute incubation instead of 3 minutes.
Tested within 2 hours – kept on ice
Normal range:
25 – 38 seconds
Clinical application:
To confirm that the prolonged aPTT is due to a deficiency in Fletcher factor (Prekallikrein)