Hemostasis+Mix Reviewer




Here's your comprehensive reviewer for Hemostasis (Cont.) & Mixing Studies:

HEMOSTASIS (CONT.) & MIXING STUDIES — Exam Reviewer

MLS 417 | BSMLS 3E

I. SUBSTITUTION STUDIES

Purpose: Detects specific clotting factor deficiencies by mixing correction reagents with patient's sample, then measuring PT and aPTT.

Key distinction from Mixing Studies:

  • Substitution Studies → detects factor deficiency ONLY

  • Mixing Studies → detects factor deficiency AND inhibitors

Reagents:

Reagent

Contains

Does NOT contain

Adsorbed Plasma Reagent (APR)

Factors I, V, VIII, XI, XII

Factors X, IX, VII, II (Vit. K-dependent)

Serum Reagent (SR)

Factors VII, IX, X, XI, XII

Factors I, II, V, VIII, XIII (consumed in clotting)

Memory tip: APR is "adsorbed" = Vit. K factors removed. SR is "serum" = clot already formed = consumed factors gone.

II. HOW TO INTERPRET SUBSTITUTION STUDY RESULTS

Step 1: Check PT and aPTT without substitution.

  • PT prolonged → Extrinsic pathway (Factor VII, III)

  • aPTT prolonged → Intrinsic pathway (XII, XI, IX, VIII)

  • Both prolonged → Common pathway (X, V, II, I, XIII)

Step 2: Apply reagents. Result is either Corrected (C) or Not Corrected (NC).

  • C = deficient factor IS present in that reagent

  • NC = deficient factor is NOT present in that reagent

Step 3: Cross-reference to isolate the deficient factor.

Quick Reference Table (Substitution Studies):

PT

aPTT

APR

SR

Pathway

Factor Deficient

N

P

C

NC

Intrinsic

VIII

N

P

C

C

Intrinsic

XI or XII (+ HMWK)

N

P

NC

C

Intrinsic

IX

P

P

C

NC

Common

V or I (additional testing needed)

P

P

NC

C

Common

X

P

P

NC

NC

Common

II

P

N

NC

C

Extrinsic

VII

Impossible pattern: PT + aPTT prolonged, with BOTH APR and SR corrected → not possible for common pathway (no factor is in both reagents). Always one or the other.

III. TESTS FOR FIBRINOLYSIS

1. Whole Blood Clot Lysis Time (WBCLT)

  • Clot incubated at 37°C; should remain intact for ~48 hours

  • Lysis < 48h = excessive primary fibrinolysis

  • More prone to inhibitors → less specific

2. Euglobulin Clot Lysis Time (ECLT)

  • Plasma diluted with water + acidified → precipitates euglobulin (removes inhibitors)

  • Contains: plasminogen, plasmin, fibrinogen, fibrinogen activators

  • Euglobulin dissolved in buffer + thrombin → observe clot lysis

  • Normal: no lysis > 2h

  • Increased fibrinolysis: lysis < 2h

  • More sensitive than WBCLT

3. Protamine Sulfate Test (PST)

  • Detects fibrin monomers (soluble fibrin monomer complexes)

  • Protamine binds to fibrin monomers → gel formation

  • Normal: no gel | Abnormal: gel forms

4. Ethanol Gelation Test (EGT)

  • Also detects fibrin monomers

  • More specific than PST (ethanol only binds fibrin monomers; protamine can bind other molecules)

  • Reagents: Ethanol + NaOH

  • Normal: no gel | Abnormal: gel forms

5. Latex D-Dimer Test

  • Detects D-dimer — specific fibrin degradation product

  • Enzyme immunoassay: antibodies specific to D-dimers → precipitation = positive

  • D-dimer is produced when plasmin breaks down a stabilized, cross-linked fibrin clot

  • Diagnostic marker for secondary fibrinolysis

  • Not specific for fibrinogen

IV. PRIMARY vs. SECONDARY FIBRINOLYSIS

Feature

Primary Fibrinolysis

Secondary Fibrinolysis

Mechanism

Plasmin attacks fibrinogen directly (no clot formed yet)

Plasmin attacks fibrin clot excessively

Fibrin clot formed?

Little to none

Yes, then broken down

Factor XIII cross-linking

Minimal/absent

Present

Coagulation activation

Minimal

Markedly activated

Diagnostic Test Results:

Test

Primary

Secondary

WBCLT

< 48h

< 48h

ECLT

< 2h

< 2h

Protamine Sulfate

Negative (–)

Positive (+)

Ethanol Gelation

Negative (–)

Positive (+)

Latex D-Dimer

Negative (–)

Positive (+)

WBCLT and ECLT cannot distinguish primary from secondary. PST, EGT, and D-dimer can.

V. MIXING STUDIES

Purpose

  • Determines if prolonged PT/aPTT is due to factor deficiency OR inhibitor

  • Usually done when aPTT is prolonged

Indications

  1. PT or aPTT is elevated

  2. No treatment with heparin or coumadin

  3. Platelet count is normal

Principle

Normal plasma contains ~100% of all clotting factors. Adding as little as 50% normal plasma to patient sample should correct a simple factor deficiency. Patient sample + Normal pooled plasma (NPP) mixed 50:50.

Mixing Study Panel:

Reagent

Contains

Does NOT contain

Fresh Plasma

All clotting factors (complete)

—

Aged Plasma

All except labile factors

Factors V, VIII

Aged Serum

Factors VII, IX, X, XI, XII, XIII

Fibrinogen group (I, II, V, VIII, XIII)

Adsorbed Plasma

Factors I, V, VIII, XI, XII, XIII

Vit. K-dependent/prothrombin group (II, VII, IX, X)

Interpretation:

  • Corrected = factor present in that reagent

  • Not Corrected = factor absent in that reagent

Correction Chart (Mixing Studies):

Factor

Fresh Plasma

Aged Plasma

Adsorbed Plasma

Aged Serum

I

C

C

C

NC

II

C

C

NC

NC

V

C

NC

C

NC

VII

C

C

NC

C

VIII

C

NC

C

NC

IX

C

C

NC

C

X

C

C

NC

C

XI

C

C

C

C

XII

C

C

C

C

XIII

C

C

C

NC

Key rule — Fresh Plasma first!

  • Fresh plasma corrected → factor deficiency → proceed to identify specific factor

  • Fresh plasma not corrected → inhibitor present → cannot identify specific factor (inhibitor interferes with the reaction)

VI. SAMPLE PROBLEM WALKTHROUGH

Problem: PT ↑, aPTT ↑ | Fresh plasma: C | Adsorbed plasma: NC | Aged serum: C

  1. PT + aPTT both prolonged → Common pathway (X, V, II, I, XIII)

  2. Fresh plasma corrected → factor deficiency (proceed)

  3. Adsorbed plasma NC → factor is absent from adsorbed plasma → absent factors: X, IX, VII, II

  4. Aged serum corrected → factor is present in aged serum → present factors: VII, IX, X, XI, XII, XIII

  5. Find the factor that is: in the common pathway + absent in adsorbed plasma + present in aged serum

    • Common: X, V, II, I, XIII

    • Absent in AP: X, IX, VII, II

    • Present in AS: VII, IX, X, XI, XII, XIII

Answer: Factor X

VII. ADSORBED PLASMA PREPARATION METHODS

Method

Key Steps

Incubation

Centrifuge

Aluminum Hydroxide

1g Al(OH)₃ + 4mL distilled water → mix 1:9 with citrated plasma

37°C, 5 min

2,500 rpm

Barium Sulfate

1mL plasma + 50mg BaSO₄

37°C, 15 min (frequent mixing)

2,000 rpm

Both methods: collect the supernatant.

VIII. QUICK MNEMONICS & TIPS

  • APR = "All Patients, Very Ill" ≈ I, V, VIII, XI, XII (no Vit. K factors)

  • SR = "Some Serum eXists" ≈ VII, IX, X, XI, XII (no consumed factors)

  • D-dimer = proof a clot FORMED then lysed → only positive in secondary fibrinolysis

  • Fibrin monomers = unstable intermediate → detected by PST and EGT

  • ECLT is more sensitive than WBCLT because inhibitors are removed

  • Factors XI and XII are in BOTH APR and SR → if both correct, those factors are excluded first

  • When both APR and SR are NC in intrinsic pathway prolongation → check for inhibitor (not just factor deficiency)

Good luck on your exam!