The presence of a factor deficiency within the intrinsic and/or common pathway may be detected by performing an APTT assay on a mixture of patient plasma and normal pooled plasma without incubation. If the correction of elevated clotting time is observed, a factor deficiency is most likely present. Failure of the normal plasma to correct the elevated APTT would suggest the presence of an inhibitor.
Send whole blood sample(s) at room temperature as soon as possible.
If specimens cannot be shipped immediately, centrifuge and separate plasma within 1 hour of collection, send frozen plasma on dry ice
APTT mixing studies are not performed:
- if the APTT falls within the normal APTT Reference Interval. See Reporting.
- if the patient is on heparin or oral anticoagulant therapy. See Reporting.