“Commonly Used Anticoagulants: EDTA, Citrates, Oxalates & Heparin – Mode of Action Explained” скачать в хорошем качестве

“Commonly Used Anticoagulants: EDTA, Citrates, Oxalates & Heparin – Mode of Action Explained”

Commonly Used Anticoagulants and Their Mode of Action Introduction Anticoagulants are substances that prevent blood from clotting by interfering with the coagulation cascade or platelet function. In laboratory hematology, anticoagulants are essential for collection, preservation, and analysis of blood samples. The choice of anticoagulant depends on the type of test to be performed, as each anticoagulant has a specific mode of action and limitations. The most commonly used anticoagulants are: EDTA Citrates Oxalates Heparin 1. EDTA (Ethylenediaminetetraacetic Acid) Forms Used Potassium EDTA (K₂EDTA, K₃EDTA) Sodium EDTA (less commonly used) Mode of Action EDTA acts by chelating (binding) calcium ions (Ca²⁺) in the blood. Calcium is an essential cofactor in multiple steps of the coagulation cascade. By removing ionized calcium, EDTA completely inhibits clot formation. Uses Complete Blood Count (CBC) Peripheral blood smear examination Reticulocyte count Hemoglobin estimation (most methods) Automated hematology analyzer testing Advantages Preserves cell morphology very well Prevents platelet aggregation Ideal for routine hematology investigations Minimal interference with cell size and shape (when used in correct amount) Disadvantages Not suitable for coagulation studies Excess EDTA causes: RBC shrinkage (false low MCV) Platelet swelling Pseudothrombocytopenia Interferes with calcium, magnesium, and iron estimation 2. Citrates Forms Used Sodium citrate (3.2% or 3.8%) Trisodium citrate Mode of Action Citrates act by reversibly binding calcium ions. Unlike EDTA, the calcium-citrate complex can be dissociated, making citrate ideal for coagulation testing, where calcium can be added back during analysis. Uses Coagulation studies: Prothrombin Time (PT) Activated Partial Thromboplastin Time (APTT) INR Erythrocyte Sedimentation Rate (ESR) – Westergren method Platelet function studies Advantages Reversible action on calcium Best anticoagulant for coagulation tests Minimal effect on coagulation factors when used correctly Disadvantages Dilutes blood (affects cell counts) Incorrect blood-to-anticoagulant ratio causes erroneous results Not ideal for routine CBC Standard Ratio 9 parts blood : 1 part sodium citrate 3. Oxalates Forms Used Potassium oxalate Ammonium oxalate Double oxalate (mixture of both) Mode of Action Oxalates prevent coagulation by precipitating calcium ions as insoluble calcium oxalate, thereby removing calcium required for clotting. Uses Previously used for ESR (Wintrobe method) Some biochemical estimations (older practice) Advantages Effective anticoagulation Stable anticoagulant Disadvantages Causes RBC shrinkage (potassium oxalate) Causes RBC swelling (ammonium oxalate) Alters cell morphology Largely replaced by EDTA and citrate in modern practice 4. Heparin Forms Used Lithium heparin Sodium heparin Ammonium heparin Mode of Action Heparin acts by activating antithrombin III, which in turn inhibits: Thrombin (Factor IIa) Factor Xa and other clotting factors This prevents conversion of fibrinogen to fibrin, thus inhibiting clot formation. Uses Blood gas analysis Biochemical investigations Cytogenetic and molecular studies Special hematology procedures Advantages Rapid anticoagulant action Does not chelate calcium Suitable for biochemical and molecular assays Disadvantages Not ideal for peripheral smear (causes blue background) May cause platelet clumping Interferes with staining quality Expensive compared to EDTA Comparative Summary Table Anticoagulant Mode of Action Common Uses EDTA Chelates calcium irreversibly CBC, blood smear Citrate Reversibly binds calcium PT, APTT, ESR Oxalate Precipitates calcium Rarely used Heparin Inhibits thrombin via antithrombin III Blood gases, biochemistry Conclusion Anticoagulants play a crucial role in hematology by preventing clot formation and preserving blood samples for accurate analysis. EDTA is preferred for routine hematology, citrate for coagulation studies, heparin for biochemical and special tests, while oxalates are now rarely used due to their adverse effects on cell morphology. Correct selection and proportion of anticoagulant are essential for obtaining reliable laboratory results.