Prothombin Time (PT) and Activated Partial
Thromboplastin Time (APTT)
Hematology Review 353
PT APTT
Purpose
Reagent(s)
Prolonged
results
Other
To detect deficiencies in extrinsic & common pathways
& to monitor coumadin (warfarin) therapy.Thromboplastin reagent (thromboplastin,
phospholipid, Ca2+).Coumadin therapy; deficiency of VII, X, V, II, or I;
circulating inhibitors.Report INR (international normalized ratio). INR =
[patient PT/mean normal PT]ISI. ISI = international
sensitivity index. Supplied by manufacturer. Be sure to
use ISI for current lot of thromboplastin & analyzer
being used. Therapeutic range for most situations is
2–3. For patients with artificial heart valves, 2.5–3.5.To detect deficiencies in intrinsic & common pathways & to
monitor unfractionated heparin therapy.Activated partial thromboplastin reagent (phospholipid,
activator), CaCl 2.Heparin therapy; deficiency of HMWK, PK, XII, XI, IX, VIII, X, V,
II, or I; circulating inhibitors.