In Case You Missed Tonight's LIVE: Recap · Microscope Views (FREE)

Marilyn Virgo

14h • General discussion

In Case You Missed Tonight's LIVE: Recap

FREE LIVE STUDY SESSION EVENING📚🧪 - December 19

VIEW RECORDING - 162 mins (No highlights)

Meeting Purpose

Review the coagulation cascade and practice ASCP exam questions.

Key Takeaways

Coagulation Cascade Basics: The intrinsic pathway (12, 11, 9, 8) handles internal vessel damage and is monitored by aPTT/PTT. The extrinsic pathway (3, 7) handles external tissue damage and is monitored by PT/INR. Both converge at the common pathway (10, 5, 2, 1).
Vitamin K-Dependent Factors: Factors II, VII, IX, and X require vitamin K for synthesis. Warfarin inhibits vitamin K, blocking these factors. Proteins C and S, natural anticoagulants, are also vitamin K-dependent.
Key Diagnostic Tests:Mixing Studies: Differentiate factor deficiencies (corrects) from inhibitors (does not correct).Bethesda Assay: Quantifies inhibitor strength after a mixing study indicates an inhibitor is present.Reptilase Time: Distinguishes heparin contamination (normal result) from a fibrinogen disorder (prolonged result) when thrombin time is prolonged.
Complex Concepts for Memorization:Lupus Anticoagulant (LA) Detection: Tests using low-phospholipid reagents (KCT, DRVVT, DTT) are more sensitive to LA because the antibody has fewer targets to bind, causing a larger effect.Time-Temperature-Dependent Inhibitors: These inhibitors (e.g., Factor VIII inhibitors) cause a mixing study to correct immediately, but then prolong again after incubation as the inhibitor activates.

Topics

Coagulation Cascade Fundamentals

Purpose: Form a blood clot to prevent hemorrhage.
Intrinsic Pathway (Internal Damage):Triggered by blood contact with a damaged vessel or foreign surface.Factors: XII → XI → IX → VIII.Monitored by: aPTT/PTT.Inhibited by: Heparin.
Extrinsic Pathway (External Damage):Triggered by tissue damage.Factors: III (Tissue Factor) → VII.Monitored by: PT/INR.Inhibited by: Warfarin.
Common Pathway:Convergence point for both pathways.Factors: X → V → II (Prothrombin) → IIa (Thrombin) → I (Fibrinogen) → Ia (Fibrin) → XIIIa (Stabilized Fibrin).
Vitamin K-Dependent Factors:Require vitamin K for synthesis: II, VII, IX, X.Proteins C and S (natural anticoagulants) are also vitamin K-dependent.Warfarin inhibits vitamin K, blocking these factors.
Factor XIII (Fibrin-Stabilizing Factor):Stabilizes the final fibrin clot.Deficiency is indicated by a clot dissolving in a 5 molar urea test.

Diagnostic Tests & Interpretation

Mixing Studies:Purpose: Differentiate a factor deficiency from an inhibitor.Method: Mix patient plasma with normal pooled plasma (NPP), which contains all factors.Interpretation:Correction: PTT returns to normal range → Factor deficiency.No Correction: PTT remains prolonged → Inhibitor present.
Bethesda Assay:Purpose: Quantify the strength of a coagulation inhibitor detected by a mixing study.
Reptilase Time:Purpose: Distinguish heparin contamination from a fibrinogen disorder when thrombin time is prolonged.Principle: Reptilase is a snake venom enzyme that converts fibrinogen to fibrin directly, bypassing the steps affected by heparin.Interpretation:Normal Reptilase Time: Prolonged thrombin time is due to heparin contamination.Prolonged Reptilase Time: Prolonged thrombin time is due to a fibrinogen disorder.
Lupus Anticoagulant (LA) Detection:Principle: LA is an antibody that attacks phospholipids. Tests using low-phospholipid reagents are more sensitive because the antibody has fewer targets, causing a larger effect.Sensitive Tests: Kaolin Clotting Time (KCT), Dilute Russell Viper Venom Time (DRVVT), Dilute Partial Thromboplastin Time (DTT).Insensitive Test: Routine aPTT (uses normal phospholipid levels).
Time-Temperature-Dependent Inhibitors (e.g., Factor VIII Inhibitors):Principle: These inhibitors require time and warmth to activate.Mixing Study Pattern:Immediate Mix: Corrects to normal (mimicking a factor deficiency).Incubated Mix: Prolongs again as the inhibitor activates and neutralizes the factors.

Random Practice Questions

T-lymphocyte maturation: Thymus.
Whole blood storage: 1–6°C.
Ascaris lumbricoides habitat: Small intestine.
Septic arthritis (<30 y/o): Neisseria gonorrhoeae.
Babesia life cycle: Resembles Plasmodium (both arthropod-borne).
Absence of Rh antigens: Rh null.
Viridans streptococci septicemia: Poor oral hygiene.
Fluoroquinolone target: Topoisomerases (enzymes for DNA replication).
Sentinel lab role: Rule out pathogens and transfer suspicious specimens; the FBI determines if a bioterrorist event occurred.