Anticoagulant prevents clotting from blood. It is used in haematological laboratory where complete blood or plasma is required; depending upon the test to be done, the type of anticoagulant is decided.
Most of the anticoagulants prevent clotting by removing calcium, or iron which are necessary for clotting process. Every anticoagulant is added in fixed proportion to blood.
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Anticoagulants are of following types:
Chemical Anticoagulant:
These anticoagulants are prepared in laboratory.
These are as follows.
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i. Citrate:
a. Trisodium citrate
b. Disodium citrate
ii. EDTA: Ethylene diamine tetracetic acid
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iii. CPD: Citrate phosphate dextrose
iv. Oxalate
Citrate:
a. Trisodium citrate:
This anticoagulant is prepared by dissolving 3.8 gm of tri-sodium citrate in 100 ml of distilled water. 0.4 ml of anticoagulant is required for 2 ml of blood. Addition of dextrose to anticoagulant provides nutrition to the red cells and helps in longer storage.
Such anticoagulant is known as Acid Citrate Dextrose (ACD) because along with citric acid, tri-sodium citrate and dextrose are mixed in this anticoagulant. This anticoagulant is used in the solution form, as it is in blood bank. The storage of blood with this anticoagulant is maximum upto 21 days.
b. Disodium citrate:
This itself provides the buffering action along with nourishment provided by dextrose. This is used in solution form. Maximum period of storage with this anticoagulant is 21 days.
EDTA (Ethylene Diamine Tetracetic Acid):
It can be prepared by dissolving 10 gm of EDTA in 1000 ml of distilled water. 0.4 ml of anticoagulant is required for 2 ml of blood. This anticoagulant does not disturb the cellular structure. Therefore, it can be used for blood cell count, ESR, prothrombin estimation, etc.
EDTA however, cannot be used for biochemical tests. This anticoagulant is dried in the container by keeping in an incubator or hot air oven for overnight period, i.e. for 12 hrs. The storage period with EDTA is 2 to 3 days.
CPD (Citrate Phosphate Dextrose):
In this anticoagulant, the citrate is dissolved in phosphate buffer, which maintains pH more accurately than ACD solution. The dextrose present in this provides nutrition to other cells. The storage period of CPD is 21 days. The disadvantage is that, it is costly and difficult to prepare and adjust pH.
Oxalate:
It is prepared by dissolving 1.2 gm of ammonium oxalate and 0.8 ml of potassium oxalate to 100 ml of distilled water 0.2 ml of anticoagulant is required for 2 ml of blood. This anticoagulant may disturb cellular structure if kept for longer period; however, if used immediately, it can be used for estimation of bilirubin, and pro-thrombin time and estimation of blood cells, PCV (Packed cell volume).
This anticoagulant is dried in a container by keeping it for overnight period in hot air oven. It is also called as double oxalate.
Biological Anticoagulant—Heparine:
Heparine is the only biological anticoagulant which cannot be prepared in a laboratory. It is obtained from leech. It is a good anticoagulant and does not alter size of RBC. It is used in concentration of 10-15 units/ml blood. This anticoagulant act by destroying thrombin or thromboplastin required for clotting.
Heparine is used to determine the blood gases. It can be used for ESR, PCV, osmotic fragility and other haematological tests.
Anticoagulant should be sterilized before use, and then blood is added to the anticoagulant, it should be mixed gently by inverting it 10 to 15 times or shacking it gently.