Evaluation Tests for Secondary Hemostasis

Activated Partial Thromboplastin Time (aPTT)

• Screening test for factors of the ____

• Monitors unfractionated _____

• Two reagents needed:

  1. ______ (kaolin, celite, silica, or ellagic acid)

  2. _____

• Principle:

  1. Add ______ reagent to _____ and incubate to allow for _____

  2. Add ____; measure the time required for clot formation.

• Screening test for factors of the intrinsic/common pathways

• Monitors unfractionated heparin therapy

• Two reagents needed:

  1. Platelet phospholipid substitute with an activator (kaolin, celite, silica, or ellagic acid)

  2. Calcium choride

• Principle:

  1. Add phospholipid/activator reagent to citrated platelet-poor plasma and incubate to allow for contact factor activation.

  2. Add calcium chloride; measure the time required for clot formation.

Activated Partial Thromboplastin Time (aPTT)

• Run normal and abnormal controls (essential for quality control).

• Reference range: _____; established by each institution

• Prolonged aPTT can indicate:

  a. Factor deficiencies in the ____; factor activity less than ____ will prolong

  b. Acquired circulating inhibitor: Heparin, ____, or antibody to a specific factor

• Run normal and abnormal controls (essential for quality control).

• Reference range: 23.0-35.0 sec; established by each institution

• Prolonged aPTT can indicate:

  a. Factor deficiencies in the intrinsic/common pathways; factor activity less than 25-30% will prolong

  b. Acquired circulating inhibitor: Heparin, lupus inhibitor, or antibody to a specific factor

Activated Partial Thromboplastin Time (aPTT)

Sources of error

• Improper sample collection, preparation, and inherent _____

  • Falsely long aPTT: Blood collection tube ____, ___ clot in tube, heparin contamination from ____, hematocrit___, and lipemia/icterus only if optical method used

  • Falsely short aPTT: ____, ___ clot in tube, and ___ containing ___ (not platelet poor)

• Incorrect _____ preparation: Incorrect dilution, water impurities, or improper storage

• _____: Problems with temperature, light source, bubbles in sample

• Improper sample collection, preparation, and inherent patient problems

  • Falsely long aPTT: Blood collection tube not full, large clot in tube, heparin contamination from line draw, hematocrit >55.0%, and lipemia/icterus only if optical method used

  • Falsely short aPTT: Hemolysis, small clot in tube, and plasma containing platelets (not platelet poor)

• Incorrect reagent preparation: Incorrect dilution, water impurities, or improper storage

• Instrumentation: Problems with temperature, light source, bubbles in sample

ProthrombinTime (PT)

• Screening test for factors of the ______

• Monitors _____ by vitamin K antagonists (_____)

• Reagents: ______ (tissue factor/TF) with _____

• Principle: Add ______ containing calcium chloride to citrated platelet-poor plasma; measure the time required for clot formation.

• Screening test for factors of the extrinsic/common pathways

• Monitors anticoagulation therapy by vitamin K antagonists (warfarin/coumarin)

• Reagents: Thromboplastin source (tissue factor/TF) with calcium chloride

• Principle: Add thromboplastin reagent containing calcium chloride to citrated platelet-poor plasma; measure the time required for clot formation

ProthrombinTime (PT)

• Reference range: _____; established by each institution

• INR: ______

  • Means of _____ reporting worldwide; not dependent on thromboplastin reagent or instrument used

  • INR values are used to monitor ____. There is no reference range. The therapeutic range is dependent on the condition being treated, but it is generally considered to be between ____.

• Formula: SEE NOTES

• Reference range: 10.0-14.0 sec; established by each institution

• INR: International normalized ratio

  • Means of standardizing PT reporting worldwide; not dependent on thromboplastin reagent or instrument used

  • INR values are used to monitor warfarin/coumarin therapy. There is no reference range. The therapeutic range is dependent on the condition being treated, but it is generally considered to be between 2.0 and 3.0.

• Formula: SEE NOTES.

ProthrombinTime (PT)

• ISI is the____ for the thromboplastin reagent this number is provided by the manufacturer and is lot number and instrument specific.

• The most sensitive thromboplastin reagents have an ISI value of _____, based on World Health Organization (WHO) standards.

• Prolonged PT can indicate factor deficiencies in the extrinsic/common pathways; factor activity less than ____ or ____ therapy will prolong the PT.

• ISI is the international sensitivity index for the thromboplastin reagent this number is provided by the manufacturer and is lot number and instrument specific.

• The most sensitive thromboplastin reagents have an ISI value of 1.00, based on World Health Organization (WHO) standards.

• Prolonged PT can indicate factor deficiencies in the extrinsic/common pathways; factor activity less than 25-30% or warfarin therapy will prolong the PT

Other Laboratory Tests

Mixing study

• is performed when the_____ is prolonged to differentiate a ____ from a ___.

• Patient plasma is mixed with ______ and test(s) is(are) repeated.

  • Shortening of the time into the reference range (correction) indicates a ____ (hereditary, or acquired causes such as warfarin therapy or liver disease).

  • Partial or no correction indicates a _____ (heparin, lupus inhibitor, VIII inhibitor, IX inhibitor).

• is performed when the PT or aPTT is prolonged to differentiate a factor deficiency from a circulating inhibitor.

• Patient plasma is mixed with normal pooled plasma and test(s) is(are) repeated.

  • Shortening of the time into the reference range (correction) indicates a factor deficiency (hereditary, or acquired causes such as warfarin therapy or liver disease).

  • Partial or no correction indicates a circulating inhibitor (heparin, lupus inhibitor, VIII inhibitor, IX inhibitor).

Other Laboratory Tests

Fibrinogen Level

• Fibrinogen level is a _____ test for fibrinogen.

• _____ is added to _____ citrated patient plasma.

• Thrombin clotting time obtained is read using a ____ and is _____ proportional to ___ concentration.

• Fibrinogen level is a quantitative test for fibrinogen.

• Thrombin reagent is added to diluted citrated patient plasma.

• Thrombin clotting time obtained is read using a standard curve and is inversely proportional to fibrinogen concentration.

Other Laboratory Tests

Thrombin Time

• Thrombin time is a _____ test for fibrinogen.

• _____ is added to _____ patient plasma and result is reported in _____.

• Presence of heparin, degradation products, or low fibrinogen level will ____ the result.

• Thrombin time is a qualitative/quantitative test for fibrinogen.

• Thrombin reagent is added to undiluted patient plasma and result is reported in seconds.

• Presence of heparin, degradation products, or low fibrinogen level will prolong the result.

Other Laboratory Tests

Factor Assay

• Factor assays are used to confirm a suspected _____, as suggested

  by a mixing study that shows correction.

• Test measures the ability of patient plasma to correct the ____ result obtained with plasma known to be factor deficient (compared to known standards).

• The _____ is reported.

• Factor assays are used to confirm a suspected factor deficiency, as suggested

  by a mixing study that shows correction.

• Test measures the ability of patient plasma to correct the PT or aPTT result obtained with plasma known to be factor deficient (compared to known standards).

• The factor activity percent is reported.

Other Laboratory Tests

5.0 M urea clot solubility test:

• The ______ that forms in factor XIII deficiency ____ in 5.0 M urea; a factor ___-stabilized clot remains intact in 5.0 M urea for at least _____.

• The unstable clot that forms in factor XIII deficiency dissolves in 5.0 M urea; a factor XIIIa-stabilized clot remains intact in 5.0 M urea for at least 24 hours.

Other Laboratory Tests

Dilute Russell viper venom test

• is a sensitive test that uses ______ as the reagent to activate factor____in the cascade.

• If the _____ is present, the venom is neutralized, and the test is prolonged

• is a sensitive test that uses snake venom as the reagent to activate factor X in the cascade.

• If the lupus inhibitor is present, the venom is neutralized, and the test is prolonged

Other Laboratory Tests

Activated clotting time (ACT)

• ______ is placed in a glass tube containing activator.

• Determine time it takes the clot to form; blood is kept at ____ during testing.

• Point-of-care test performed at a clinic, cardiac catheterization laboratory, or surgical suite.

• Most often used to monitor _____ during coronary artery bypass surgery.

• Whole blood is placed in a glass tube containing activator.

• Determine time it takes the clot to form; blood is kept at 37°C during testing.

• Point-of-care test performed at a clinic, cardiac catheterization laboratory, or surgical suite.

• Most often used to monitor high-dose heparin therapy during coronary artery bypass surgery.