8.1 - LABORATORY TESTS TO EVALUATE SECONDARY HEMOSTASIS (PART 2)

Single Factor Assay Procedure

Used to confirm a suspected factor deficiency, as suggested by mixing study shows correction

Factor VIII deficiency (Hemophilia A)

Factor IX deficiency (Hemophilia B)

Factor XI deficiency (Rosenthal syndrome)

Single Factor Assay Procedure is used in (3)

Monitoring/Documentation of therapy

Clinical use of Single Factor Assay Procedure

Percentage of factor activity

Reporting of result for Single Factor Assay Procedure

Fibrinogen Assay

Acute phase reactant

Pregnancy

Inflammatory states

Stress

Oral contraceptives

Liver disease (moderately severe)

Hypofibrinogenemia (<200 mg/dL)

DIC and severe liver disease

Fibrinogen Assay is elevated in (7)

Precipitation and denaturation

Turbidimetric or fibrin clot density

Coagulable protein assay

Immunologic assays

Methods of Measurement in fibrinogen assay (4)

Heparin levels greater than 0.6 u/mL

FDP levels greater than 100 microgram/mL

False decrease fibrinogen result

mg/dL of fibrinogen

Fibrinogen Assay reporting of results

Circulating Inhibitors/Circulating Anticoagulants

Causes prolonged PT or APTT but is not corrected by addition of fresh plasma

Lupus Anticoagulant

Non-specific inhibitors

Lupus Anticoagulant

IgG immunoglobulins directed against a number of phospholipid-protein complexes (Xa-Va-calcium-platelet phospholipid)

Specific inhibitors

IgG immunoglobulins directed against specific coagulation factors

Anti-factor VIII

the most common of the specific inhibitors; detected in 10% to 20% of patients with severe hemophilia

Anti-factor IX

detected in 1% to 3% of factor IX-deficient patients

PTT Mixing Studies

Mix patient sample with normal sample

LAC

Specific factor inhibitors

Factor deficiency

PTT Mixing Studies is used to detect and differentiate: (3)

heparin

pooled normal PPP

coagulation factor deficiency

1-2, 37

PTT Mixing Studies

1. TCT is performed to rule out _

2. If no heparin is present, the patient's PPP is mixed with equal amounts of _ _ _, and PT is performed

   • Note: If the mixture PTT corrects to within 10% of the PNP PTT (or to within the reference interval) and the patient is experiencing bleeding, a _ _ _ (coagulopathy) is presumed

3. 2nd aliquot of pt. PPP and reagent. PPP is incubated for _-_ hrs at _ C

Note: If after the 1-2 hrs incubation, the PT result is corrected, the originally prolonged PTT result is caused by a factor deficiency

Correction

Factor Deficiency: Correction/No correction

No correction

Lupus-like anticoagulant, Factor IX inhibitor, heparin: Correction/No correction

Correction

Factor VIII inhibitor: Correction/No correction

XII

1. Px: No manifestation of bleeding

   • Several family members are treated for thrombotic episodes

   • Laboratory Results:

     • Bleeding time: Normal

     • PT: Normal

     • PTT: Prolonged

     • PTT 1:1 mixing study: Correction

       • Intrinsic pathway

   • Based on the laboratory results, what factor deficiency is expected?

1. XII

2. VIII

3. XIlI

4. II

Presence of circulating inhibitors

1. Hemorrhagic Px

   • Laboratory Results:

     • Bleeding time: Normal

     • PT: Normal

     • PTT: Prolonged

     • PTT 1:1 mixing study: No Correction

• Intrinsic Pathway

• Fresh plasma was not able to correct the PTT

• Problem here is the inhibitors

• These laboratory results are most consistent with:

1. Hemophilia A (F VIII)

2. Presence of circulating inhibitors

3. Warfarin Therapy

4. Hemophilia B (F IX)

Hemophilia A (F VIII)

1. Severe Hemorrhagic Px

   • Laboratory Results:

     • Bleeding time: Normal

     • PT: Normal

     • PTT: Prolonged

     • PTT 1:1 mixing study: Correction

       • Hemorrhagic Px are more associated with Factor VIII deficiency

   • These laboratory results are most consistent with:

1. Hemophilia A (F VIII)

2. Presence of circulating inhibitors

3. Warfarin Therapy

4. Hemophilia C (F XI)

Nijmegen-Bethesda Titer for Anti-Factor VIII Inhibitor

Used to confirm and quantify specific anti-factor VIII inhibitor

Quantitated by mixing the test plasma with known factor VIII

After incubation, residual Factor VIII is measured by specific factor assay

Nijmegen-Bethesda Titer for Anti-Factor VIII Inhibitor

Amount of inhibitor present: Calculated by comparing the VIII activity in the patient incubation mixture with that of the control mixture