COMMON TESTS FOR SECONDARY HEMOSTASIS Flashcards by pattie o.

Reagent for ‘partial’ in aPTT uses

phospholipid portion of tissue thromboplastin

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aPTT reagent is derived from

brain or plant phospholipids

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Primary improvement of aPTT over PTT

Complete contact activation by adding an activator, shortening PTT and narrowing the normal range

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Examples of solid particulate activators used in aPTT

Silica, kaolin, celite, bentonite

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Example of a soluble activator used in aPTT

Ellagic acid

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Reference range for aPTT (general)

35 to 45 seconds

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Specimen requirements for aPTT testing

Citrated platelet-poor plasma (<15,000/uL platelets) prepared by centrifugation

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Components of the aPTT reagent

(1) Platelet substitute (phospholipid) and (2) Activator

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Role of CaCl2 in aPTT testing

Re-calcifies the plasma to allow coagulation

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Temperature requirement for aPTT testing

37°C (water bath)

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Therapy monitored using aPTT

Unfractionated heparin (UFH) therapy

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Pathways evaluated by aPTT

Intrinsic (VIII, IX, XI, XII) and common pathways (II, V, X, I)

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Factors that can indicate coagulation deficiencies detected by aPTT

Common factors (II, V, X, I) and intrinsic pathway factors (VIII, IX, XI, XII)

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Time for clotting to occur in aPTT test

Measured in seconds, reported to the nearest tenth

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Component added after incubation in aPTT testing

Warmed CaCl2

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Standard reference range for aPTT

35 to 45 seconds (generally)

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Reference range for PT (generally)

10-13 seconds

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Type of test for PT, aPTT

Clot-based coagulation screening test

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Specimen requirements for PT testing

Citrated platelet-poor plasma (<15,000/uL platelets) prepared by centrifugation

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Materials required for PT testing

Thromboplastin-Calcium Chloride (CaCl2) reagent (PT reagent; Simplastin)

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Required equipment for PT testing

Test tubes (12 X 75-mm glass tubes), Pipets, 37°C water bath

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Control material purpose in PT testing

Ensures validity and accuracy of test results

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Primary use of PT

Monitors warfarin therapy

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Pathways detected by PT

Common and extrinsic pathways

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Procedure step in PT testing involving reagent temperature

Warm PT thromboplastin reagent at 37°C for 3 to 5 minutes

Volume of PT reagent added to plasma sample

0.2 mL of PT reagent to 0.1 mL of plasma

Unit for reporting PT results

Seconds

Alternative ways to report PT results

Patient time with control time, Patient time with reference range, Prothrombin ratio, INR

Purpose of INR (International Normalized Ratio)

Standardizes PT reporting to correct for variability in thromboplastin sensitivities

Calculation for prothrombin ratio

PT of patient divided by mean reference range, multiplied by 100

Key use of INR

Corrects for variability in PT results due to different thromboplastin agents

INR calculation requirement for Coumadin therapy

Calculated only for patients with a stable anticoagulation response

PT result interpretation during the first week of Coumadin therapy

Interpreted in seconds and compared with the reference interval

Target INR range for most indications

2.0 to 3.0

Target INR range for patients with a mechanical heart valve

2.5 to 3.5

Purpose of INR

Minimizes differences in PT results due to different reagent-instrument combinations

Formula for calculating INR

Patients PT / Mean normal PT ^ ISI

Definition of ISI in INR calculation

International Sensitivity Index

Interpretation of ISI values for thromboplastin reagents

ISI < 1.0 for more sensitive reagents, ISI > 1.0 for less sensitive reagents

Effect of more sensitive thromboplastin reagents on PT

Results in longer PT

Effect of less sensitive thromboplastin reagents on PT

Results in shorter PT

Coumarin drugs are Vitamin K antagonists (VKAs) that interfere with the synthesis of clotting factors

II, VII, IX, X, Proteins C and S

Examples of coumarin drugs include dicumarol, phenprocoumon, acenocumarol, and the most commonly used drug

Warfarin

Warfarin interferes with the synthesis of these clotting factors and proteins

Factors II, VII, IX, X, and Proteins C and S

Reversal agents for warfarin overdose include

Vitamin K (oral/intravenous), Fresh-frozen plasma, Prothrombin complex concentrate, Recombinant activated factor VII (rVIIa)

Forms of Vitamin K used to reverse warfarin overdose

Oral Vitamin K, Intravenous Vitamin K

Options to reverse a warfarin overdose depending on patient condition

Vitamin K (oral/intravenous), Fresh-frozen plasma, Prothrombin complex concentrate, Recombinant activated factor VII (rVIIa)

UFH acts as an anticoagulant by accelerating the binding of this protein to target enzymes

Antithrombin

UFH is routinely used in this medical procedure

Cardiac surgery

UFH therapy requires monitoring with these assays

Partial thromboplastin time (PTT), Activated clotting time (ACT)

UFH is administered via this route

Intravenously

Protamine sulfate neutralizes UFH. It is a protein extracted from this source

Fish sperm (salmon sperm)

ACT (activated coagulation time) is an example of this type of test

Clot-based coagulation screening test

ACT is a point-of-care assay used in these settings

Clinics, inpatient’s bedside, cardiac catheterization laboratory, surgical suite

ACT is specifically useful in monitoring this aspect of UFH therapy

High UFH dosages

ACT test procedure involves adding this to blood and recording the clotting interval

Particulate activator

LMWH is produced by this process

Controlled fragmentation of heparin

LMWH primarily inhibits this factor, but not thrombin

Activated factor Xa (factor Xa)

LMWH is administered via this route

Subcutaneous injection

LMWH has a lower incidence of this compared to unfractionated heparin

Heparin-induced thrombocytopenia

LMWH has a lower incidence of these compared to unfractionated heparin

Hemorrhage, osteoporosis

One disadvantage of LMWH compared to unfractionated heparin

Increased cost

One disadvantage of LMWH compared to unfractionated heparin

More complicated monitoring

Mechanical/Electromechanical examples of coagulation instrumentation

BBL fibrometer and Diagnostica Stago analyzers

Uses electromechanical clot detection system that measures a change in conductivity between two metal electrodes in plasma

BBL fibrometer

Uses the detection of the oscillation of a steel ball within the plasma-reagent solution. Viscosity starts to increase as fibrin strands form, slowing the movement

Diagnostica Stago analyzers

Principle used in photo-optical coagulometers

Detects a change in plasma optical density during clotting

Modification of photo-optical end-point detection used in nephelometric coagulometers

90-degree or forward-angle light scatter is measured instead of optical density

Substrate used in chromogenic (amidolytic) coagulation assays

Synthetic oligopeptide conjugated to a chromophore, usually para-nitroaniline (pNA)

Advantage of chromogenic assays in evaluating patients on anticoagulants or with inhibitors

Inhibitors do not interfere with the chromogenic assay

Coagulation instrumentation based on antigen-antibody reactions

Immunologic coagulometers

Russel’s viper venom function

Bypasses Factor VII and directly activates Factor X to Xa

Stypven time use

Helps differentiate Factor VII and Factor X deficiencies

Normal Stypven time value

20 to 25 seconds

Dilute Russel’s Viper Venom Time (dRVVT) purpose

Detect lupus anticoagulants

Normal dRVVT value

30 to 35 seconds

Thrombin Time (TT) purpose

Detect low fibrinogen, impaired fibrinogen function, presence of heparin, fibrin(ogen) degradation products, and streptokinase

Thrombin Time sensitivity

Sensitive in detecting heparin inhibition

Normal Thrombin Time value

15 to 18 seconds

Reptilase Time purpose

Converts fibrinogen to fibrin; unaffected by heparin

Reptilase is an enzyme found in

Bothrops atrox snake

Normal Reptilase Time value

10 to 15 seconds

Thrombin Time and Reptilase Time in Hypofibrinogenemia

Both prolonged

Thrombin Time and Reptilase Time in Immunologic Antithrombin

Thrombin time prolonged, Reptilase time normal

Thrombin Time and Reptilase Time in Heparin Therapy

Thrombin time prolonged, Reptilase time normal

Clotting Time Slide/Drop Method procedure

Perform skin puncture, transfer blood drop, check for fibrin strands every 30 secs

Normal Clotting Time Slide/Drop Method value

2 to 4 minutes

Normal Clotting Time Lee and White Method value

7 to 15 minutes