Anticoagulants : Composition, Action, Merits & Demerits…..

Anticoagulants are the chemicals which prevent clotting of blood when mixed with blood in proper proportion.

Action of Anticoagulants :

1. Some anticoagulants prevent clotting of blood by precipitating ionic calcium (Ca⁺⁺) in the plasma.
2. Heparin act as an anti-thrombin to prevent the transformation of prothrombin to thrombin and thus prevent the formation of fibrin from fibrinogen.

Anticoagulants used in Laboratory and in Blood Bank  :

• Following anticoagulants are uses in the laboratory for examination of blood.:

1. 1. Sodium Fluoride
   2. Heparin
   3. Ethyl Diamine Tetra Acetic acid (EDTA)
   4. Sodium Citrate
   5. Potassium ammonium oxalate (Double Oxalate) etc.

• Following anticoagulants are uses in the Blood Bank for preservation of blood components; these are generally not used in the haematological investigations.
  1. Acid Citrate Dextrose (ACD)
  2. Citrate Phosphate Dextrose (CPD)
  3. Citrate Phosphate Dextrose Adenine (CPDA)
  4. RBC suspension in saline, adenine, glucose and manitol mixture. etc.

Merits & Demerits of Anticoagulants

Sodium Fluoride

• Composition : Di-sodium or di-potassium salts.
• Merits :  It prevents glycolysis by inhibiting the enzyme system involved in glycolysis.
• Demerits :
  • It not suitable for enzyme determination and also for urea determination.
  • It is also not suitable for urgent test report because time requires obtaining plasma is 15 – 30 minutes.

Heparin

• Composition : It is available as Sodium (Na), Potassium (K), Lithium (Li) and ammonium (NH₄).
• Mechanism of action : It prevents coagulation of blood by acting as an anti-thrombin to prevent the transformation of prothrombin to thrombin and thus prevent formation of fibrin from fibrinogen.
• Merits :
  • Heparin used in the treatment of different thrombotic disorders.
  • It used for Osmotic fragility test and electrolyte estimation.
• Demerits :
  • It is an expensive anticoagulant and it action is short duration (4 - 6 hrs.).
  • Heparin should not be used for haematological investigation since it produced a blue back-ground in the smear.
  • It inhibits Acid phosphatase (for prostate), Lactose dehydrogenate (LDH), and affects the binding of T₃ and T₄ to their carrier proteins.
• Dose :
  • 15 ± 2.5 IU/ml of blood (for investigation).
  • 0.5 – 1.0 mg/kg (for treatment).

Ethyl Diamine Tetra Acetic acid (EDTA)

• Composition : It is used as disodium and dipotassium salts.
• Mechanism of action : It acts as a chelating agent. The calcium of the blood is bound in a unionized and soluble complex with EDTA anticoagulant.
• Merits :
  • EDTA anticoagulant preserved the cellular components well, so it is used for many haematological investigations.
  • It inhibits the clamping of platelets; hence it is preferred for Platelet count.
• Demerits :
  • It is not suitable for Calcium and Iron analysis using colorimeteric method
  • EDTAantcoagulant inhibits the enzymes such as alkaline phosphatase and creatinine kinase.
• Dose : 2 mg/ ml of blood

Sodium Citrate

• Composition : It is used as 0.106(M) Tri-sodium citrate or Sodium citrate.
• Mechanism of action : It acts as calcium chelating agent as like EDTA.
• Merits :
  • 3.2 % Sodium Citrate is mainly used for coagulation studies because it preserves labile pro-coagulant.
  • 3.8% Sodium Citrate is used full for ESR estimation by Westergren method.
• Demerits :
  • It inhibits enzymes activity of SGPT, SGOT and ALP.
  • It interferes in the determination of Calcium and Inorganic phosphate.
• Dose :
  • For Coagulation studies : 1 part of citrate solution with 9 parts of blood.
  • For ESR estimation : 1 part of citrate solution with 4 parts of blood.

Potassium ammonium oxalate (Double Oxalate)

• Composition : 3 parts of Ammonium oxalate and 2 parts of Potassium oxalate.
  • Ammonium oxalate    : 2.4 gm
  • Potassium oxalate       : 1.6 gm
  • Distilled water               : 100 ml
• Mechanism of action :  Oxalate combined with calcium in the blood to form insoluble precipitate of calcium oxalate.  Three (3) parts of Ammonium oxalate and Two (2) parts of Potassium oxalate are combined together to balance swelling effects of ammonium oxalate and shrinking effects of  potassium oxalate on the red blood cells.
• Merits :
  • Balanced part of ammonium oxalate and Potassium oxalate preserves the shape of the erythrocyte; hence it is used for haematology.
  • Potassium oxalate in-combination with Sodium fluoride, used for blood glucose estimation.
  • It is used for TLC, TRBC, PCV, MCV, MCH, MCHC, Haemoglobin, ESR (by Westergren method) determination in the blood.
• Demerits :
  • It inhibits several enzymes such as Acid phosphatase, Amylase, Alkaline Phosphatase and also interferes in Calcium determination.
  • This anticoagulant is not used for determination of morphology of the WBC; hence not used for blood smear preparation.
  • It id toxic and since calcium oxalate precipitate may causes herm. It is never used for Blood Banking and for blood transfusion.
• Dose : 2 mg / ml of blood