Calcium, Ionized (Serum)

Additional Information:

UFHPL Epic order code: LAB5227

CPT Code(s):


Specimen Requirements:

Type: Serum

Note: SEND A SEPARATE TUBE for ionized calcium and adhere a piece of labeling tape over the top of the tube with the following written on it “Ionized Calcium − DO NOT OPEN.”.

Note: No isotopes should be administered to the patient within 24 hours prior to the venipuncture.

Container/Tube: Gel-barrier tube

Sample Volume: 1 mL

Storage: Do not freeze specimens.

Stability (collection to time of analysis/testing):

  • Ambient: 14 days
  • Refrigerated: 14 days
Rejection Criteria:

  • Hemolysis
  • Opened gel-barrier tube
  • Gel-barrier not completely sealing the clot
  • Plasma specimen


Evaluate nonbound calcium, calcium metabolism, physiologically active calcium fraction, hyperparathyroidism, ectopic hyperparathyroidism. Occasionally useful when hypercalcemia coexists with abnormal protein state, such as myeloma. Useful in assessing active calcium fraction in hypoproteinemia and acidosis when calcium is low.


Total calcium remains the first-line test for the evaluation of calcium abnormality.


Ion-selective electrode (ISE)

Reference Values:

Reference Interval: 4.5 – 5.6 mg/dL