TABLE 36-2
Common Tests of Hemostatic Function (
continued)
Test Name
Description
Component Measured
Sensitivity
Common Use
Interferences/Complications
Plasma Coagulation Factors— Anticoagulant Subsystem Components
Protein C
Determ ination o f the activity
Other vitam in K-dependent
o f Protein C
proteins, especially in
sam ples from patients
Determ ination o f the
receiving vitamin K
amount o f Protein C
antagonist oral
antigen
anticoagulants. In som e
tests that use aPTT or PT
based procedures
dependence on Factor VIII
and Factor V exists.
Determ ination o f a possible
cause o f throm bosis, or
thrombotic risk, performed
only in specialized
laboratories
Oral anticoagulant therapy.
Different procedures are
inconsistently biased by the
decreased y carboxylation
o f Protein C and the other
vitam in K-dependent proteins
Protein S
Determ ination o f the activity
(ability) o f Protein S to
enhance the activity o f
activated Protein C
Determ ination o f the
amount o f Protein S antigen
C4b binding protein can
affect the assay, only free
Protein S is measured
C4b binding protein can
affect the assay
Determ ination o f a possible
cause o f throm bosis, or
identification o f thrombotic
risk, performed only in
specialized laboratories
Oral anticoagulant therapy,
Factor V R506(2 (Factor V Leiden),
anti-phospholipid antibodies
(lupus anticoagulants)
APC R esistance A ssay
Determ ination o f the ability
o f activated Protein C to
inactivate Factor Va in
patients in w hich the
Protein C activity is normal
The m ost com m on assay is
a m odified aPTT. Elevated
levels o f Factor VIII bias the
assay results, as do
decreased levels o f vitamin
K-dependent factors.
Determ ination o f a possible
cause o f thrombosis. M ay
be used as a screen for
w om en on oral
contraceptives w ho are
suggested to have other
risk factor for thrombosis.
Oral anticoagulants, unless a
dilution is m ade into
Factor V -deficient plasm a
and a variation on a factor V
specific assay is needed
Antithrombin
Determ ination o f the activity
(functional concentration) o f
anti thrombin
M inim al other com ponent
sensitivity because o f the
use o f exogenous thrombin
or Factor Xa. C linically
antithrombin levels m ay be
low ered by liver disease
Determ ination o f the cause
o f throm bosis, risk o f
throm bosis in patients with
history o f thrombosis
Heparin cofactor II m ay interfere,
bovine thrombin m inim izes this
interference
(continued)
