Chemical agents that prevent coagulation are routinely used when whole blood or plasma is required. Some of the commonly used anticoagulants are:
(1) Heparin (2) Salts of Ethylene diamine tetra
acetic acid (EDTA)
Heparin
It is the most widely used anticoagulant and causes least
interference with tests. It is available as sodium, potassium, lithium and
ammonium salts. This anticoagulant accelerates the action antithrombin III
which neutralizes thrombin and prevents conversion of fibrin form
fibrinogen.
It is used in 0.2mg/ml
blood. Its disadvantage is high cost and short action, and produces blue
background in blood smears. It is believed to inhibit the activity of acid
phosphatase and affect binding of T3 and T4 to carrier proteins producing high
free concentrations of these hormones.
EDTA
It is a chelating agent useful in hematology as it preserves
the cellular component of blood. It is used as disodium, dipotassium or
tripotassium salt. It is used as 1-2mg/ml blood. EDTA prevents coagulation by
chelating calcium.
Dry EDTA vials are used. It by chelating metallic cofactors,
inhibits alkaline phosphatase, creatine kinase and other enzymes. It is not
suitable to use in specimen for calcium and iron analysis.
Sodium fluoride
It is used when blood is collected for glucose estimations. It is a weak anticoagulant but is often added as preservative
for blood glucose together with potassium oxalate as anticoagulant. It is
effective at a concentration of 2mg/ml blood. It inhibits the enzyme enolase
(sodium fluoride) thus inhibiting glycolysis. Na fluoride/K oxalates are mixed
in the ratio 1:3.
Citrate
Sodium citrate solution at concentration 3.8g/dl in ratio or
1 part to 9 part of blood is widely used for coagulation studies because its
effect is reversible by addition of calcium.
Oxalates
Sodium, potassium, ammonium, and lithium oxalates inhibit
blood coagulation by forming insoluble complex with calcium. Potassium oxalate
at concentration of 1-2 mg/ml of blood is widely used. Combined ammonium and/or
potassium oxalate does not cause shrinkage of erythrocytes. It consists of three parts by weight of
ammonium oxalate, which causes swelling of the erythrocytes, balanced by two
parts of potassium oxalate which causes shrinkage. NH4+ & K+ oxalate
mixture in the ratio of 3:2, and 2 mg / ml of blood is the required amount.
The disadvantage of the use of oxalate is
the alteration of concentrations of plasma components. Shrinkage of erythrocytes results from a
water shift from the erythrocytes to plasma. This shift increases with
increasing anticoagulant concentration, and if used in the same concentration
on a weight basis, all anticoagulants will have this effect inversely
proportional to their molecular weight.
Aside from the water shift there may be alteration of erythrocyte
permeability, which may explain the varied and inconsistent effects of oxalates
and other salt anticoagulants on certain plasma constituents. Because of the difficulty, at times, in
obtaining satisfactory preparation of heparin commercially, Heller and Paul
introduced in 1934, a balanced oxalate mixture for use in hematocrit and sedimentation
rate determinations. It consists of
three parts by weight of ammonium oxalate, which causes swelling of the
erythrocytes, balanced by two parts of potassium oxalate which causes
shrinkage.
Iodoacetate
Sodium iodoacetate at concentration
of 2mg/ml is an effective antiglycolytic agent and a substitute for sodium
fluoride. It is a potent (suicide) inhibitor of G3P dehydrogenase
Formalin, toluene, 6N HCl, Boric acid, thymol, chloroform are
used as urine preservatives for 24 hour urine.
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