Posted on 29th March 2011 by admin in Uncategorized

When blood samples are collected blood coagulation is activated due to the intrinsic pathway that is triggered by contact with negatively charged surfaces such as glass.  This is why blood begins to coagulate in a test tube.  To prevent blood from clotting anticoagulant substances can be added.  There are two methods a coagulant can use to prevent blood clotting.  It can either chelate or precipitate calcium from the blood making it unavailable to the coagulation process or it can inhibit the formation of thrombin that is needed to convert fibrinogen to fibrin during the coagulation process.  An anticoagulant should be added to whole blood specimens immediately after collection to prevent microclot formation.

There are several different types of anticoagulants that can be used for different types of testing.  There are four common anticoagulants that are used for certain types of testing.

EDTA- This anticoagulant is a sodium or potassium-based salt that is used to prevent coagulation by binding calcium.  Many blood banks use it when collecting blood from donors.  It is also used because it is able to preserve cell morphology and inhibit platelet aggregation for hematology tests.

Citrates- Citrates are able to prevent coagulation by binding calcium.  Sodium citrate is used for coagulation tests because it is very effective at preserving the coagulation factors of the blood, which are performed on plasma.  In order to add this anticoagulant to plasma the specimens must be centrifuged so that the plasma is separated from the cells.  Calcium is added back to the specimen to initiate clotting during testing.  As the calcium is added the clotting process is timed.

Heparin- This anticoagulant is used to prevent clotting by inhibiting the formation of the enzyme thrombin.  This enzyme is necessary for clot formation.  As with other anticoagulants, heparin should be mixed into a collected specimen immediately to prevent clot formation and fibrin generation.  There are three heparin formulations that are used to prevent clotting.  They are ammonium, lithium, and sodium heparin.  The most commonly used formulation is lithium heparin because it causes the least interference in chemistry testing and widely used for plasma and whole-blood chemistry tests.

Potassium oxlates- Oxlates are able to precipitate calcium from the blood.  The most commonly used oxalate is potassium oxalate, which is often used to provide plasma for glucose testing.

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