Anticoagulants
are the chemicals which prevent clotting of blood when mixed with blood in
proper proportion (Willard et al; 1999). These chemicals, apart from hepian works
by binding calcium ions preventing coagulation proteins from using them.
Heparin interferes with the formation and/or activity of thrombin and the
activity of clothing factor 1X, X, XI, XII (Hylek et al; 2007).
Characteristics
of anticoagulants;
An
anticoagulant selected for use in hematological examination must have the
following qualities;
1.
It
must not alter the size of red cells
2.
It
must not cause haemolysis
3.
It
must minimize platelet aggregation
4.
It
must minimize disruption of the staining and morphology of leukocytes
5.
It
must be readily soluble in blood. (Schalm et al; 2006).
The
Frequently used anticoagulants includes;
1.
Ethylenediaminetetra acetic acid (EDTA)
2.
Oxalate
3.
Heparin
4.
Sodium citrate
5.
Sodium fluoride/potassium oxalate
6.
Citrate phosphate dextrose and adenine
(CPD-A).
7.
Fluoride oxalate (FO)
8.
Acid citrate dextrose (ACD)
Ethylenediaminetetra
acetic acid, heparin, fluoride oxalate and sodium citrate are the ones will be
used for the study and hence they are explained below;
Ethylenediaminetetra
Acetic Acid (EDTA)
EDTA
is a widely used acronym for the chemical compound Ethylenediamintetra acetic
acid. EDTA is a polyamino carboxylic acid with the formular (CH2N)
CH2 CO2H2)2. The colorless, water
soluble solid is widely used to dissolved scale. Its usefulness arises because
of its role as a chelating agents, that is its ability to “sequester” metal
ions such as Ca2+ Fe3+. After being bound by EDTA metal
ions remain in solution but exhibit diminished reactivity. EDTA is produced as
several salts; notably disodium EDTA and calciumdisodium.
EDTA
(Vitalongevity
2007). (Jain 2006) said that EDTA consist or comes in 2 forms;
a.
The
tripotassium salt (K3 EDTA)
b.
And
the disodium salt (Na2 EDTA). He also added that the potassium salts
(Liquid or dry powder) are used in commercial tubes because they are more
soluble. (Calcium EDTA is not used as an anticoagulant, but in the treatment of
lead poisoning).
Synthesis of EDTA;
The
compound was first described in 1935 by Ferdinard Munz, who prepared the
compound from ethylenediamine and chloroacetic acid (Vitalongevity 2007).
Today, EDTA is mainly synthesized from ethylenediamine (1,2-diamino ethane),
formaldehyde (Methanal), and sodium salt which can be converted in a subsequent
step in the acid forms;
H2NCH2CH2NH2+4CH2O+4NaCN+4H2O®(NaO2CCH2)2NCH2
CH2N (CH2CO2Na) 2 + 4NH3
(NaO2CH2
NCH2)2 NCH2 CH2N (CH2 CO2Na)2
4HCI® (HO2CCH2)
2 NCH2 CH2N(CH2CO2H2+4NaCL.
Impurities
cogenerated by this route include glycine and niterilotriacetic acid (New
York Times; 2008).
Mode of Action
It acts as a powerful calcium chelating agent. The calcium in blood is
bound in an unionzed and soluble complex with EDTA
Tests which are
performed by using EDTA blood are:
1.
Haemoglobin
2.
White
blood count
3.
Packed
cell volume determination
4.
Erythrocyte
sedimentation rate by wintrobe’s method
5.
Platelet
count
6.
Differential
white blood cell count
7.
Advantages
1.
It
gives the best preservation of cellular morphology. Good morphology of the cell is observed even
after 2 to 3
hours of blood collection
2.
Since platelet clumping is inhibited for
platelet counts using this anticoagulant is preferred (Willard et al 1999)
Disadvantages;
1.
Excess EDTA causes shrinkage of red blood
cells and erroneous packed cell volume, mean cell volume and means corpuscular
haemoglobin (Jain 2006).
2.
Platelets
swell and disintegrate due to excess of EDTA and artificially high platelet
count may be obtained due to disintegrated platelets.
3.
EDTA
is not suitable for use in the
coagulation studies mainly in the
determination of prothrombin time
4.
EDTA
2k (potassium salt is recommended as anticoagulant for complete blood count. (Willard et al 1999)
Mechanism of Action of Anticoagulants
The thromboplastin released by damaged tissue, or platelets converted inactive
prothrombin into active thrombin in the
presence of calcium ions. Thrombin coverts soluble fibrinogen into insoluble
fibrin clot in the presence of calcium ions.
Thromboplastin
Prothrombin -------------------> Thrombin
Ca++
Thrombin
Fibrinogen(soluble) -------------------> Fibrin
(insoluble)
Ca++
fibrin + blood cells clot (fine threads)