Calcium, Ionized

Test Code

CPT Codes

Preferred Specimen
2 mL serum collected in a serum separator tube

Minimum Volume
0.6 mL

Instructions: Collect blood (2 mL serum) in a gel barrier tube. Let clot and spin immediately with cap on. Do not open tube. Ship the unopened gel barrier tube at room temperature. Do not freeze.

Transport Container
Serum Separator Tube

Transport Temperature
Room temperature

Specimen Stability
Room temperature: 7 days
Refrigerated: 7 days
Frozen: Unacceptable

Ion Specific Electrode (ISE)

Setup Schedule
Set up: Daily evening; Report available: Next day

Reference Range
<8 Months  Not established
8 Months-10 Years 4.9-5.4 mg/dL
11-17 Years 4.8-5.3 mg/dL
Adult 4.8-5.6 mg/dL

Clinical Significance
The ionized calcium is determined by an ion selective electrode methodology. The result that is generated is pH adjusted. The result is empirically based on a measured pH and ionized calcium concentration normalized to a pH of 7.40. This calculation compensates for in vitro changes in pH due to loss of CO2 through specimen handling. Ionized calcium represents the true "bioavailable" calcium in the circulation. In situations where the total calcium is normal but does not fit the clinical picture, e.g., hyperparathyroidism, a determination of the ionized calcium will, many times, show an elevation in the "bioavailable" calcium component. This may be due to alterations in protein concentrations, especially albumin, that binds most of the calcium in the circulation.

Performing Laboratory
Quest Diagnostics Nichols Institute
14225 Newbrook Drive
Chantilly, VA 20153

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.