Coagulation - Blood Collection:
Plasma is used to minimize the time needed for coagulation so it is used is medical emergencies.
There are many types of anticoagulants used nowadays for example:
- Heparin (salt of mucoitin polysulforic acid) is widely used and causes the least interference with the tests. About 20 units of heparin is needed to anticoagulate 1 ml of blood.
- Ethylenediaminetetraacitic acid (EDTA): this chelating agent is presented as salt with final effective concentration of 1-2 mg/ml of blood. It should not be used for specimens tested for calcium analysis.
- Sodium fluoride: this is generally considered as a preservative of glucose (it inhibit enzyme system involved in glycolysis); however it has weak anticoagulant activity. Fluoride at a concentration of about 2 mg/ml is the best preservative for glucose. Most specimens are preserved at 25 oC for 24 hr or 4 oC for 48 hr. Urea can not be estimated (in urease based methods) in a sample with fluoride because it inhibit the enzyme urease.
- Other anticoagulants used are for example sodium citrate, oxalates, and iodoacetate.
For estimation of bicarbonate in blood, it should be collected under one inch column of liquid paraffin to avoid exposure to the atmosphere, before it is centrifuged and processed. This is to avoid escape of carbon dioxide.