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16
Chapter 2
•
Cardiovascular Care
Evaluating Lipid Test Results
COAGULATION TESTS
Test
Action
Elevated Levels
Normal Range
International
Normalized
Ratio (INR)
INR is the
preferred
test and best
standardized
measurement
of PT.
The INR system was
established to reduce the
interlaboratory variation in
prothrombin time.
The INR is calculated as a
ratio of the patient’s PT to
a control PT obtained using
an international reference
thromboplastin reagent
developed by the World
Health Organization (WHO).
Used for monitoring warfarin
(Coumadin) treatment.
Increased INR values may
indicate disseminated
intravascular coagulation
(DIC), liver disease,
antiphospholipid antibodies,
vitamin K deficiency,
or uncontrolled oral
anticoagulation
In healthy people an INR of 1.1
or below is considered normal.
An INR range of 2.0 to 3.0
is generally an effective
therapeutic range for people
taking warfarin for disorders
such as atrial fibrillation or a
blood clot in the leg or lung.
In certain situations, such as
having a mechanical heart
valve, you might need a slightly
higher INR.
Prothrombin
time test (PT)
Assesses the clotting ability
of blood. A prothrombin time
within this range indicates
that the patient has normal
amounts of clotting factors
VII and X.
A prolonged PT time is
considered abnormal
11–15 sec
Activated Partial
Thromboplastin
Time (aPTT)
aPTT is sensitive to the
deficiencies or abnormalities
of both intrinsic and common
coagulation factors, i.e.,
Factors I, II, V, X, VIII, IX, XI, XII,
Fletcher factor, and Fitzgerald
factor.
The activated partial
thromboplastin time (aPTT,
PTT) measures the time it
takes plasma to clot when
exposed to substances that
activate the contact factors,
which assesses the intrinsic
and common pathways of
coagulation
When the aPTT is prolonged,
there is an inhibitor present
in patient’s plasma.
29–35 sec
Thrombin Time
(TT)
The thrombin time (TT)
measures the final step of
coagulation, the conversion
of fibrinogen to fibrin
Thrombin time is prolonged
in the presence of heparin,
hypofibrinogenemia,
dysfibrinogenemia, and fibrin
degradation product
15–17 sec