Heparin_{(Heparin )} is an anticoagulant commonly used in chemistry and specially chemistry testing and routine clinical chemistry determination. It is the recommended anticoagulant for many determinations using whole blood or plasma specimens because of its minimal chelating properties, minimal effects on water shifts, and relatively low cation concentration.

Heparin_{(Heparin )} is the only anticoagulant that should be used in a blood collection device for the determination of pH, blood gases, electrolytes and ionized calcium. Heparin should not be used for coagulation or hematology testing.

Three salts of heparin_{(Heparin )} that are commonly used in blood collection devices: lithium and sodium and amonium.

Although all of the 3 salts of heparin_{(Heparin )} give comparable results for electrolyte determinations, lithium heparin has been favored over the others, because of the perception that sodium heparin might overestimate sodium levels and ammonium heparin might spuriously increase serum urea nitrogen concentrations when measured by the urease procedure.

Lithium heparin is therefore the recommended form of heparin_{(Heparin )} to be used because it is least likely to interfere when performing tests for other ions. Lithium heparin is essentially free of extraneous ions. It should not be used for collection of blood for lithium levels.