The salts of the chelating (calcium-binding) agent EDTA are recommended by the International Council for Standardization in Haematology (ICSH) and CLSI as the anticoagulant of choice for blood cell counting and sizing because EDTA causes less shrinkage of RBCs and less increase in cell volume on standing. The laboratory procedure manual should specify the specific type of anticoagulant required for a procedure. To avoid the introduction of errors into test results, the proper proportion of anticoagulant to whole blood must be used. Each type of anticoagulant prevents whole blood coagulation. Tripotassium ethylenediaminetetraacetate (K3 EDTA), dipotassium ethylenediaminetetraacetate (K2 EDTA), sodium citrate, and heparin are examples of commonly used anticoagulants.

Inorganic additives, biochemical additives, and gel in blood collection tubes come in a variety of forms.

The use of additives at the proper concentration in evacuated tubes improves the accuracy and consistency of test results while also allowing for faster turnaround times in the laboratory. The additives range from those that promote faster blood clotting to those that preserve or stabilize specific analytes (such as glucose) or cells. Evacuated blood collection tubes without anticoagulant are used to produce serum (or as a discard tube), whereas other types of evacuated tubes may contain an anticoagulant or additive.

Additive sequence of an array