Coagulation and fibrinolysis II - PT, PTT, TT

What is the factor with the highest concentration in the plasma?

fibrinogen (I)

What are the three steps of fibrin clot formation?

1. proteolytic cleavage of alpha and beta subunits off of the E nodule

2. Spontaneous polymerization of the fibrin monomers

3. fibrin stabilization with covalent bonds and alpha-2-antiplasmin from XIIIa

How do we collect for coagulation tests (what sample and what tube)?

Collect whole blood in light blue sodium citrate top

Why is it important that the light blue top (citrate) is filled exactly to the marker on the tube?

special ratio of whole blood to citrate (9:1) for proper coagulation testing

What increased false results may occur due to improper blood:citrate ratios?

1. low blood:citrate ratio due to improper filling

2. high hematocrit

3. EDTA contamination from EDTA tubes

What is the PT test? What does it measure?

PT = prothrombin test

PT measures the time for a fibrin clot to form

What pathways does the PT test evaluate?

Extrinsic and common

What factor deficiencies can prolong a PT test?

VII, X, V, II, and I

What reagents are used in a PT test?

TF (tissue factor, also known as thromboplastin) and calcium

What is the reference range of PT test?

12-15 seconds

What is stypven time? What does its reagent substitute for in a PT test?

Measures the formation of a fibrin clot, just like PT

uses Russells viper venom instead of TF to bypass factor VII

What is an international normalized ratio (INR)?

The prothrombin time ratio that reflects the results that would be obtained by WHO

What is the international sensitivity index (ISI)?

a value assigned by the manufacturer to thromboplastin reagent for its activity

What is the formula for INR?

INR = (PT of patient/PT of normal range mean)^ISI

What are the therapeutic ranges of INR?

patients NOT on oral anticoagulant: INR < 1.1

Patients ON warfarin: 2 < INR < 3

Patients on Coumadin: 2.5 < INR < 3.5

Panic value: INR > 3.5

What is aPTT or PTT test? What does it measure?

aPTT or PTT = partial prothromboplastin time test

measures fibrin clot formation

What pathways does the PTT evaluate?

Intrinsic and common

What factor deficiencies can prolong PTT?

XII, XI, IX, VIII, X, V, II, and I

What reagents are used in PTT?

phospholipids, kaolin, and calcium chloride

What is the reference range of PTT?

25-35 seconds

What is TT test? What does it measure?

TT = thrombin time test

measures the conversion of fibrinogen to fibrin

What specific factor does it evaluate?

fibrinogen (I)

What are the reagents used in TT?

commercial thrombin (IIa)

What conditions may prolong TT?

heparin administration, increased fibrin degradation products, deficient fibrinogen, or dysfunctional fibrinogen

If a patient is on heparin, what test may replace the TT test?

Reptilase R test

What is the quantitative fibrinogen assay? What does it measure?

determination of fibrinogen concentrations

measures clot times against a standard curve

What is the reference range of the TT test?

15-19 seconds

What is the reference range of quantitative fibrinogen assay?

200-400 mg/dL

What is the heparin inactivation test? When is this test used?

use of heparinase to degrade heparin

Used when a prolonged PTT time occurs, could be due to heparin medication or contamination

What is the anti-Xa assay? What reagent is used and what does it measure?

used for monitoring patients on heparin

measures reverse proportion of heparin (Xa conc.) by binding Heparin ATIII to Xa

Which factors are non functional if vitamin K is not present?

X, IX, VII, II

What are some anticoagulatns that decrease vitamin K?

warfarin, Coumadin,

What is an anticoagulant that inhibits thrombin and Xa?

Heparin

What are some natural inhibitors of coagulation?

antithrombin III

What is the function of protein C?

inhibiting vitamin K which inhibits VIIa and Va

What is the function of protein S?

vitamin K inhibitor and cofactor of protein C