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Test Code LAB4041 CALCIUM, IONIZED

Important Note

The tube should be filled completely to limit the loss of CO2.

Specimen Type

Preferred Specimen: Lithium Heparin Whole Blood (Dark Green Top)

Alternative Specimen: Heparinized Syringe

Specimen Volume

2 mL

Minimum Volume

1 mL

Turnaround Time

STAT: 10 minutes
Routine: 30 minutes

Test Schedule

Daily

Sample Stability

Room Temp: 30 min

On Wet Ice or Refrigerated: 24 Hours

Method

ISE

Reference Ranges

Normal:  4.75 - 5.30

Critical:  < 3.3 and > 6.2

Synonyms

IONIZED CALCIUM

iCal

Free calcium

CPT Codes

82330

Test Components

Calcium, Ionized, mg/dL;

Specimen Processing

Do not place specimen on ice if it will be analyzed within 30 minutes. If specimen cannot be analyzed within 30 minutes, store and transport on ice water.

Collection Instructions

Collect and handle anaerobically. The tube should be filled completely to limit the loss of CO2.

Test Limitations

Bedrest for 3 days or more may elevate ionized calcium into the abnormal range. Within the pH range of 7.2-7.6 the normalized calcium value included in the report represents what the ionized calcium concentration would be if the pH of the sample was 7.4 For specimens with pH values outside the 7.2-7.6 range, only the ionized calcium value will be reported since the pH is out of range to calculate the normalized value. This ionized calcium result alone may not reflect the physiologic calcium status due to the pH of the specimen. In rare instances where either the ionized calcium or the pH is beyond the range of the instrument (i.e., ionized calcium 20 mg/dL, and pH < 6.0 or > 8.8), no results will be reported.

Clinical Information

Ionized calcium, which accounts for 50% to 55% of total calcium, is the physiologically active form of calcium.

Low ionized calcium values are often seen in kidney disease, critically ill patients, or patients receiving rapid transfusion of citrated whole blood or blood products.

Increased serum ionized calcium concentrations may be seen with primary hyperparathyroidism, ectopic parathyroid hormone-producing tumors, excess intake of vitamin D, or various malignancies.

Nomograms have been used to calculate ionized calcium from total calcium, albumin, and pH values. However, calculated ionized calcium results have proven to be unsatisfactory. A Mayo study of 114 patients found significant differences between ionized and total calcium in 26% of patients.