Laboratory Evaluation of Secondary Hemostasis

Study Notes

Clotting Time Assessment

Tilt tube #1 at 45° after 5 minutes to initiate clot formation, wait 30 seconds for interval.
Clotting time observed in tube #3 is recorded.

Activated Clotting Time (ACT)

Utilized for monitoring patients on heparin therapy.
Incorporates an activator and samples incubated at 37°C.
Normal reference values differ for general patients and those undergoing heparin therapy.

Plasma Recalcification Test

Involves adding 0.025 M CaCl2 to the sample.
Requires citrated Platelet Poor Plasma (PPP) or Platelet Rich Plasma (PRP) for testing.
Reference values vary for PPP and PRP.

Activated Partial Thromboplastin Time (aPTT)

Monitors efficacy of heparin therapy and screens for deficiencies in intrinsic and common clotting pathways.
Thromboplastin consists of lipoprotein and phospholipids.
Uses citrated PPP as the specimen.
Main reagents include aPTT reagent with rabbit phospholipids, assorted activators, and 0.025 M CaCl2.
Reference range must be established for patient assessment.

Extrinsic Pathway Evaluation

Influenced by Vitamin K deficiencies and oral anticoagulants.
Quick’s Test/Prothrombin Time (PT) is essential for monitoring oral anticoagulant therapy.
Detects deficiencies related to Vitamin K-dependent clotting factors, excluding factor IX.
Requires citrated PPP and PT reagent for testing.
Reference range influenced by the International Sensitivity Index (ISI) with WHO standard set at 1.0.

Secondary Hemostasis Overview

Assesses presence and functionality of coagulation factors in cascade reactions post-injury.
Fibrin clot stabilization necessitates coagulation factors once a platelet plug forms.

Intrinsic and Common Pathways Assessment

Intrinsic factors include XII, XI, IX, VIII, High Molecular Weight Kininogen (HMWK), and Prekallikrein (PK).
Common factors encompass X, V, II, I, and XIII.
Disorders in these pathways are often tied to liver diseases, circulating anticoagulants, and conditions like hypofibrinogenemia and lupus inhibitors.

Clotting Time Evaluation Methods

Slide/Drop Method: For children, involves capillary puncture; starts timing after the second blood drop and waits 30 seconds for fibrin formation.
Capillary Tube Method (Dale and Laidlaw’s Method): Blood is placed in a tube with no anticoagulant; check for fibrin formation every 30 seconds post skin puncture.
Lee and White Whole Blood Coagulation Time: Less sensitive to factor deficiencies; begins timing when 1 mL of blood is transferred to individual tubes. Excessive sample agitation may lead to false results.

Description

This quiz covers the laboratory tests used to evaluate secondary hemostasis, including the presence of coagulation factors and their function in the cascade reaction. It also explores the role of coagulation factors in stabilizing platelet plugs and forming fibrin clots.