Ordering Recommendation

Use to assess calcium status.

New York DOH Approval Status

This test is New York state approved.

Specimen Required

Patient Preparation

Serum separator tube.

Specimen Preparation

Do not open the tube or split the specimen. Do not freeze separator tube. Do not expose specimen to air at any time during collection or transport process.  Centrifuge with stopper in place within one hour of collection. Transport 5 mL serum in original serum separator tube. (Min: 0.5 mL)

Storage/Transport Temperature

Refrigerated. Ship upright in original serum separator collection tube  and transport in the ARUP shipping rack. Do not ship on dry ice.

Unacceptable Conditions

Plasma and samples exposed to air in aliquot tubes.  Frozen specimens.


Ambient: 24 hours; Refrigerated: 1 week; Frozen: Unacceptable


Ion-Selective Electrode/pH Electrode




Within 24 hours

Reference Interval

Ionized calcium (ISE):
1.09-1.30 mmol/L

Ionized calcium (calculation at pH 7.4):
1.09-1.30 mmol/L

Interpretive Data

Compliance Category



Differences between the ionized calcium result and the ionized calcium normalized to pH 7.4 are due to the sample having a pH significantly different from pH 7.4.  Specimen pH may be artificially decreased due to delayed processing and may be increased when the specimen is exposed to air.  Due to these factors, it is recommended that the ionized calcium normalized to pH 7.4 be interpreted with caution and only used when the clinician has knowledge of the patient's acid/base status.  Accurate determination of in vivo pH is best determined by arterial blood gas testing.

Hotline History


CPT Codes



Component Test Code* Component Chart Name LOINC
0020136 Calcium, Ionized Serum 12180-6
0020138 Calcium Ionized pH 7.4 19072-8
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.


  • CA Ionized, Serum
  • Ca2+
  • Free Calcium
  • Ionized Calcium
Calcium, Ionized, Serum