Coagulation Testing and Treatments Flashcards
Collection
Must be first tube, recommended anticoagulant is 3.2% trisodium citrate
Required Volume Ratio
Blood must be collected in an ratio of 9:1 and the fill volume must be at least 90% of the target volume.
-If patient has a hematocrit greater than 0.55, the PT and APTT may be affected
Storage
-PT/INR: kept at 18-24c and tested within 24 hours of collection
-APTT for non-heparinized patients: 2-3 or 18-24c, test within fur hours of collection
-APTT testing for unfractionated heparin : kept at 2-4 or 18-24c, centrifuged within one hour and tested within four hours from collection
Prothrombin Time (PT/INR) Purpose
Purpose: evaluation of bleeding, detection of factor deficiencies, assessment of liver disease, and
monitoring of oral anticoagulation (warfarin) therapy.
Prothrombin Time : Principle
Principle: This test measures the extrinsic and common pathways of coagulation. The test starts with
addition of thromboplastin (tissue factor plus phospholipid) with the addition of CaCl2.The time to formation
of a fibrin clot is measured by either an optical or mechanical method. The rapidity of clotting is the result
of tissue factor complexing with factor VII and direct activation of factor X.
Prothrombin Time (PT/INR) : Sample Type
Sample: typically performed on platelet-poor plasma sample that is anticoagulated with 3.2% sodium
citrate to chelate calcium. PT/INR testing may be tested up to 24 hours from the collection time, provided
the sample is un-centrifuged or centrifuged with plasma remaining on top of cells
Prothrombin Time (PT/INR) : Clinical Significance
Clinical utility: to detect the deficiency of one or more of the clotting factors of the extrinsic pathway of the
coagulation cascade. A prolonged PT indicates deficiencies of plasma factors VII, X, V, II, or fibrinogen, as
well as inhibitors to these factors.
Activated Partial Thromboplastin Time (aPTT): Purpose
Purpose: to screen for inherited and acquired coagulation disorders, as well as to monitor unfractionated
heparin therapy
Activated Partial Thromboplastin Time (aPTT): Principle
Principle: This test measures the intrinsic and common pathways of coagulation. Performed by recalcifying plasma in the presence of standardized amount of platelet-like phosphatides and an activator of
the contact factors of the intrinsic pathway. aPTT can detect deficiencies of all clotting factors except
factors VII, and XIII. The result is usually normal if all coagulation factors are present in a concentration
greater than 30%. The result will be prolonged in the presence of heparin, direct thrombin inhibitors, or
circulating anticoagulants such as lupus-like anticoagulant or specific factor inhibitors
Activated Partial Thromboplastin Time (aPTT) : Clinical Utility
Clinical utility: to monitor heparin and direct thrombin inhibitor anticoagulant therapy, screen for von
Willebrand disease and coagulation factor deficiencies in the intrinsic and common pathway (fibrinogen,
and factors II, V, VIII, IX, X, XI, XII, pre-kallikrein, and high-molecular-weight kininogen). It is a preoperative screen for competence of a patient’s ability to clot and is useful for detection of lupus
anticoagulant and other coagulation inhibitors.
Thrombin Time (TT): Purpose
Purpose: to assess fibrinogen activity.
Thrombin Time (TT): Principle
Principle: This test measures the time for clot formation when thrombin is added to citrate plasma.
Thrombin catalyzes the conversion of fibrinogen to fibrin, by cleaving fibrinopeptides A and B.
Polymerization of fibrin to form a clot occurs. By adding exogenous thrombin, the intrinsic, extrinsic and
common pathways are bypassed. A normal result requires release of fibrinopeptides from fibrinogen and
unimpeded polymerization of fibrin monomers
Thrombin Time (TT): Clinical Significance
Clinical utility: to screen samples with a prolonged aPTT result for heparin contamination and will be
prolonged in:
◊ Hypofibrinogenemia
◊ Abnormal fibrinogen (dysfibrinogenemia)
◊ Presence of fibrinogen or fibrin split products which inhibit the conversion of fibrinogen to fibrin
◊ Presence of heparin-like anticoagulants
◊ Presence of inhibitors to thrombin, such as direct thrombin inhibitor drugs
◊ Presence of high levels of immunoglobulin paraprotein which can interfere with fibrin formation
Fibrinogen Assay : Purpose
Purpose: to determine low functional levels seen in disseminated intravascular coagulation (DIC), massive
bleeding, and liver disease
Fibrinogen Assay: Principle
Principle: measures the qualitative amount of fibrinogen in patient’s plasma. The Clauss method
measures the rate of clot formation after adding a high concentration of thrombin to citrated plasma. The
fibrinogen activity of the sample is derived from a standard curve relating the clotting time to plasma
standards of known fibrinogen activity
Fibrinogen Assay: Clinical Utility
Clinical utility: useful in diagnosis of dysfibrinogenemia and hypofibrinogenemia, diagnosis of DIC, liver
failure, and primary fibrinolysis, and guiding transfusion therapy with cryoprecipitate.
