TABLE 36-2
Common Tests of Hemostatic Function
Test Name
Component Measured
Common Use
Plasma Procoagulants
Activated Clotting Tim e
A form o f an aPTT performed
using w hole blood
Heparin m onitoring in the
operating room
Insensitive to low m ol wt
Thrombin Tim e
Functional evaluation o f
fibrinogen concentration,
polym erization
Fibrinogen ‘concentration’
and fibrin functionality
(fibrinopeptide cleavage,
fibrin polym erization)
Heparin causes artifactual
prolongation because o f
enhanced thrombin
inactivation by antithrombin
Specific Factor A ssays
Factor VIII
Factor IX
Other Factors
Evaluation o f the
functional concentration
(activity) o f individual
factors, specificity created
by using specific factor
deficient plasmas.
C om m only performed as
an aPTT-like assay
Sensitivity is to the factor
m issing from the
particular deficient plasm a
Estim ation o f the activity
level o f a particular factor
D ifferences m ay be
observed betw een deficient
plasm as from individuals
with hereditary deficiencies
and im m unodepleted
plasm as
Primary Hemostasis, Cellular Components
Platelet Count
D irect determination o f the
number o f platelets per unit
volum e
Platelet number
D iagnosis o f
throm bocytopenia
Generally none, but insensitive
to defective function
B leeding Time
M easurement o f vW F
function, platelet function
and indirect m easure o f
platelet count and
Platelet count, vW F
function (multimers) and
platelet function
General hem ostatic
function, without platelet
count interpretation cannot
be made
Interpretation requires an
independently determined
platelet count
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