TABLE 36-2
Common Tests of Hemostatic Function
(continued)
Test Name
Description
Component Measured
Sensitivity
Plasma Coagulation Factors— Anticoagulant Subsystem Components
(c o n tin u e d )
Heparin
Determination o f the
functional concentration o f
heparin
Specific heparin assays
em ploy either exogenous
thrombin or Factor Xa.
E xogenous antithrombin
m ay also be added to
ensure that only heparin
is measured
Plasma Coagulation Factors—Fibrinolytic System Components
Plasm inogen/Plasm in
Determination o f fibrinolysis
Plasm in inhibitors
or plasm in hydrolysis o f a
(antiplasm in)
peptide chrom ogenic
substrate
Fibrin D -D im er
Plasm inogen Activator(s)
Immunoassay, formats are
ELISA and latex
agglutination
Functional assay-PA ’s
circulate in an active form
and are released by blood
pressure cu ff com pression,
the activator’s ability to
convert plasm inogen into
plasm in is measured
Determination o f the amount
o f tPA antigen by ELISA
Fibrin
A ffected by plasm inogen
activator inhibitors (PA I’s)
Show substantial diurnal
variation
A ffected by plasm inogen
activator inhibitors
(PAI’s) Plasm inogen
(antibody specificity),
glycosylation o f tPA
Common Use
Interferences/Complications
M onitoring “standard”
heparin and low m ol wt
heparins. Routine heparin
m onitoring is com m only
done using the aPTT, but
the aPTT is insensitive to
the new low m ol wt
heparins. C om m on OR
procedure in surgeries
em ploying extracorporeal
circulation
M onitoring o f fibrinolytic
therapy, evidence o f
ongoing fibrinolysis,
decreased levels o f
plasm inogen
Determination o f ongoing
fibrinolysis and its extent,
evidence for thrombosis
M onitoring o f fibrinolytic
therapy, determination o f
possible cause for
thrombosis or risk factor
for thrombosis, m ay be
useful in predicting ischem ia
Possible cause for
thrombotic risk,
performed only in
specialized laboratories
Heparin binding to thrombin
(if thrombin is used) can cause
biased results.
Throm bin-based assays are
poorly sensitive to low m ol wt
heparins
Incom plete activation o f
plasm inogen by streptokinase,
com peting inactivation reaction
with inhibitors
Fibrin degradation products that
contain the D fragment
Inactivation by inhibitors,
m inim ized by collection into pH
6
buffer (without pH
6
, values are as
low as
1 / 1 0
normal values)
Prolonged cuff pressure
C om plicated by the presence o f
tPA and T P A -P A I1 com plexes
(
continued)
