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Test Code 168 Calcium, Ionized

Additional Codes


PowerChart: Calcium Ionized

Specimen Requirement

Venous or Arterial lithium heparin whole blood is required.

Additional Specimen Collection Information

Collect blood in a lithium heparin, green-top tube. Plasma gel tubes are NOT acceptable. Collection tubes must be filled to capacity. Samples must be run within 10 minutes of collection; avoid exposing samples to air. Venous whole blood is the only acceptable sample type.

Note: Full heparin microtainers are acceptable. (DO NOT overfill or underfill)

Useful For

Assessing calcium states during liver transplantation surgery, cardiopulmonary bypass, or any procedure requiring rapid transfusion of whole blood in neonates and in critically ill patients.


Testing is performed Monday through Sunday.

Typically completed within 30 minutes after the specimen arrives at the testing site.

CPT Code Information

82330 Chemistry: Calcium, ionized

LOINC Code Information

17864-0 Calcium.Ionized [Mass/Volume] In Serum Or Plasma By Ion-Selective Membrane Electrode (ISE)

Test Method

Ion-Selective Electrode Potentiometry; iSTAT

Reference Values

1.12-1.32 mmol/L

  • Critical Value:
    • Low: < 0.80 mmol/L
    • High: > 1.60 mmol/L

Venous stasis (prolonged tourniquet application) and forearm exercise may increase ionized calcium due to a decrease in pH caused by localized production of lactic acid. Exposing the sample to air will cause an increase in pH due to the loss of CO2, which will decrease ionized calcium.


Heparin binds calcium. Each unit of heparin added per ml of blood will decrease ionized calcium by 0.01 mmol/L. Therefore, the correct ratio of heparin anticoagulant to blood must be achieved during sample collection. Intravenous injection of 10,000 units of heparin has been shown in adults to cause a significant decrease of ionized calcium of about 0.03 mmol/L.


Hemodilution of the plasma by more than 20% associated with priming cardiopulmonary bypass pumps, plasma volume expansion or other fluid administration therapies using certain solutions may cause clinically significant error on ionized calcium results. These errors are associated with solutions that do not match the ionic characteristics of plasma. To avoid these errors when hemodiluting by more than 20%, use physiologically balanced multi-electrolyte solutions containing low-mobility anions (e.g. Gluconate) such as Normosol-R (Abbott Laboratories), Plasma-Lyte-A (Baxter Healthcare oCrporation), and Isolyte-S (B Braun Medical) rather than solutions such as normal saline or ringer’s lactate.

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