coagulation studies Flashcards
Coagulation occurs when
blood vessel has been injured, and the
body is attempting to stop excess bleeding
activated by damage to blood vessel
Factors XII, XI, IX, VIII
Intrinsic pathway
Hemostatic process
- Vasoconstriction: vasospasm to reduce blood flow
- Platelet aggregation: adhere to site to form temporary plug
- Clotting factor activation: leads to formation of fibrin clot
Vit-K dependent factors, anabolic steroids, Vit
K, digitalis, benadryl, OCPs
Shortened PT
triggered by tissue injury and exposure to tissue
factor III and factor VII
Extrinsic pathway
both intrinsic and extrinsic paths converge
Factor X, V, prothrombin (II), fibrinogen (I)
common pathway
- Measures the extrinsic and common pathways (factors I, II, V, VII, X)
- Normal range: 11-13.5 seconds
- Critical >20 seconds
- Used to monitor warfarin therapy
Prothrombin Time (PT)
conversion of fibrinogen to fibrin to form stable clot
final stage
can suggest deficiencies in extrinsic pathway
factors (VII) or presence of inhibitors (Warfarin, liver disease
Prolonged PT
- Measures the intrinsic and common pathways (factors I, II, V, VIII, IX, X, XI,
XII) - Normal range: 25-35 seconds
- Critical >70 seconds
- Used to monitor heparin therapy
o Heparin inactivates prothrombin and prevents formation of thromboplastin
Activated Partial Thromboplastin Time (aPTT)
When an activator is added, PTT is known as
aPTT
can indicate intrinsic pathway issues
(hemophilia, factor deficiencies) or the presence of inhibitors
(heparin, lupus anticoagulant)
o Cirrhosis of liver, Vit K deficiency, DIC, heparin
Prolonged aPTT
early stages of DIC, extensive cancer
Decreased aPTT
Activated Partial Thromboplastin Time (aPTT) interfering factors
antihistamines, ascorbic acid, heparin,
salicylates
A standardized method of expressing PT, used to
monitor warfarin therapy
International Normalized Ratio (INR)
International Normalized Ratio (INR) normal range
- Normal range: 0.8-1.2 (for healthy individuals)
- Critical >5
- Therapeutic range for anticoagulation: 2.0-3.0
(depends on the indication) - High INR indicates risk for bleeding
- Measures the conversion of fibrinogen to fibrin (assesses
fibrinogen levels) - Abnormalities may indicate fibrinogen deficiency or the presence
of inhibitors (anticoagulants like heparin)
thrombin time (TT)
- Normal: 70-120 seconds, on anticoagulant: 150-600 seconds
- Indications: To measure anticoagulant effect of heparin or other
thrombin inhibitors
o Cardiac angioplasty
o Hemodialysis
o Cardiopulmonary bypass surgery - Pathophys: Measures the time it takes for whole blood to clot after
addition of particulate activators
o Like aPTT = Measures intrinsic pathway but more accurate than APT at high doses of heparin
o Can monitor the response of unfractionated heparin therapy
o Can determine amount of protamine sulfate needed to reverse effects of hepar
Activated Clotting Time (ACT)
ACT
* Interfering factors
hypothermia, hemodilution, platelet number
and function, pharmacokinetics of heparin, partially or completed
occluded specimens
ACT increased
heparin, clotting factor deficiencies, cirrhosis,
coumadin, lupus inhibitors
ACT decreased
thrombosis
more useful than aPTT when high doses are use
ACT
o During cardiopulmonary bypass surgery
* ACT is less expensive and can be done more easily and rapidly
at bedside
- Normal: <0.4 mcg/mL
- Indications: intravascular clotting
- Pathophys: Assesses both the thrombin and plasmin activity
o Degradation product of fibrin as plasmin acts on the fibrin polymer clot
o Provides a highly specific measurement of the amount of fibrin
degradation that occurs - Interfering factors: decreased in lipemic patients, increased if
rheumatoid factor (RF) is >50 IU/mL (normal <20
D-Dimer
D-Dimer
* Increased:
o DIC
o Primary fibrinolysis
o DVT
o PE
o Arterial thromboembolism
o Sickle cell anemia with or without crisis
o Malignancy, pregnancy, surger
Age and physiological factors
Neonates and infants may have different normal values
- Decreased D dimer
Lipemic patients
Thrombophilia testing
Inherited conditions like protein C/S deficiency, factor V Leiden, and antiphospholipid
syndrome
Bleeding disorders
- Hemophilia A and B (Factor VIII and IX deficiences)
- Vitamin K deficiency (involves factors II, VII, IX, X)
- Liver disease (impairs synthesis of coagulation factors)
- Disseminated intravascular coagulation (DIC)
Medication interference:
- Heparin contamination can prolong PT and aPTT
- Warfarin therapy affects PT/INR
Monitoring anticoagulation therapy
- Warfarin (PT/INR)
- Heparin (aPTT)
Incorrect blood sample handling
Hemolysis can falsely prolong PT and aPTT
* Inadequate volume or improper anticoagulant use can affect results
