Quantitative determination of Activated Partial Thromboplastin
Test (APTT)
IVD
Store at 2-8ºC
PRINCIPLE OF THE METHOD
Citrated plasma, a contact activator, and procoagulant phospholipids
(partial thromboplastin of animal origin) are mixed and incubated at
37ºC. The contact agent activates the contact system, including high
molecular weight kininogen, prekalilkrein, Factor XI, and Factor XII. The
phospholipid provides a surface for interaction of coagulation factors. After
incubation, an appropriate concentration of calcium ions is added, and time
to clot formation is measured. Calcium ions are required to assemble the
complex for activation of the intrinsic coagulation cascade subsequent to
Factor XIa.
CLINICAL SIGNIFICANCE
Activated partial thromboplastin time (APTT) test is one of the most common
coagulation tests used in any coagulation laboratory. This test is used for
diverse purposes of preoperative screening, screening for coagulation
factor deficiency, screening for various types of coagulation inhibitors
(e.g. lupus anticoagulants) and for controlling heparin therapy.
The APTT is a measure of the integrity of the intrinsic and final common
pathways of the coagulation cascade. The APTT represents the time, in
seconds, for patient plasma to clot after the addition of phospholipid, an
intrinsic pathway activator (such as silica, celite, kaolin, ellagic acid), and
calcium (to reverse the anticoagulant effect of the oxalate-citrate in the
collection tube).
APTT reagent is called partial thromboplastin because tissue factor is not
present in conjunction with the phospholipid as it is in the PT reagent.
Thus, deficiencies or inhibitors of clotting factors within the intrinsic and
final common pathways result in prolongation of the APTT.
SAMPLES
Handle blood samples as potentially infectious. Label sample tubes
correctly, respecting the patient’s privacy, with unequivocal tracking to the
test request form including full patient information. It is recommended that
blood specimens be collected by venipuncture using a blood collection
system that collects the specimen directly into glass or plastic evacuated
tube containing sodium citrate as anticoagulant. Discard clotted samples
and tubes that have been over or under filled: it is important that 9 parts of
blood are mixed with 1 part of sodium citrate solution (0.11 mol/L).
PROCEDURE
The reagent can be used by manual method, mechanical, photo-optical or
other means of clot dete.
