Heparin, is a natural anticoagulant in
the body found in the liver (from the Greek word” hepar” meaning liver)
and may also be within basophils
and mast cells. Heparin is also called anti thromboplastin or antithrombin (Schalms; 2006)
Heparin is isolated from either porcine intestine or form beef lung where it is bound to histamine and
stored in the mast cell granules, when heparin is isolated, the
purification leads to a heterogeneous mixture of molecules it is an
acidic polysaccharide with side groups, either
sulpates or N-acetyl groups attached to
individuals sugar
group. The sulfate groups are extremely important in the anticoagulant
activity by binding to antithrombin III (at III) enhancing the rate of thrombin
–Antithrombin III complex formation by 1,000 to 10,000 fold. (platelet
inhibitors, com/review article).
Heparin is available in a liquid or dry
form as sodium, calcium, ammonium and lithium salts, each of these will interfere
with determination of their respective
ions in the plasma.
Mode of action; it interferes
with the formation and / or activity of
thrombin
and the activity of clotting factors IX, X, XI, XII. (Schalms; 2006).
Lithium or sodium salt
of pheparin at a concentration
of 10 20ul per ml of blood is a commonly used
anticoagulant for chemistry, gas analysis and emergency tests. It does not
alter the size of the red cells, and it is recommended when it is important to
reduce to a minimum the chance of
lysis occurring after blood has
been drawn. It is thus the best anticoagulant for osmotic fragility test and is
suitable for immuniphenotyping (Dacie and Lewis; 2008).
However, heparin is not suitable for
blood counts because it often induces platelet and leucocyte clumping (Van
and Simmons; 1995, Salzamin and Rosenberg; 1980, and Hirsh and Levine; 1992).
Disadvantages of
Heparin Anticoagulant,
1.
It
causes clumping of leucocytes
2.
It
interferes with the staining of leucocytes
3.
It
is the most expensive of anticoagulants
4.
Blood
will clot within 8-12 hours because clotting is only delayed but
not prevented
5.
It
is not suitable for agglutination tests, coagulation studies (prothrombin time tests or plasma fibrinogen
determination )
6.
It
may interfere with some automated biochemical analyses of plasma (Schalms; 2006).
In a study carried out by Mahony
and Fergusm; 1992 they found that heparin and
other calcium - chelating anticoagulants have differing effects on
platelets but no consensus was reached.
Platelets tends to Clump in samples
collected into low molecular weight heparin (LMWH) precluding its use as an anticoagulant
cited from (Am Jvet Res, 2001) . This was contrary to what (Nwafia et al
2003) got in their study, they concluded from their study that there
is minimal loss of platelet in blood
stored in heparin when compared
to other anticoagulants used in
their study and
said heparin have sparing effect on platelets (Nwafia et al, 2003).