{"id":"calcium-ionized","name":"Calcium, Ionized","shortName":"Ionized Calcium","aliases":["Ionized Calcium","Free Calcium","iCa","Calcium Ionized, Serum","Ionized Ca","Ionised calcium","Calcium, Ionized, Serum","Calcium, Ionized, Whole Blood","Ionized Calcium, Whole Blood","Calcium, Free","Calcium Unbound","Calcium Filterable","Ionized calcium (iCa)","Calcium Ionized pH 7.4","Calcio ionizado","Calcio iónico"],"abbreviations":["iCa","Ca2+"],"loinc":[{"code":"17864-0","primary":true},{"code":"17863-2","primary":false},{"code":"1995-0","primary":false},{"code":"12180-6","primary":false},{"code":"19072-8","primary":false},{"code":"1994-3","primary":false}],"specimen":"serum-or-plasma","units":[{"ucum":"mg/dL","display":"mg/dL"},{"ucum":"mmol/L","display":"mmol/L"}],"referenceRanges":[{"population":"24–97","low":4.57,"high":5.43,"unit":"mg/dL","unitDisplay":"mg/dL","note":"Mayo Clinic Laboratories prints 4.57–5.43 mg/dL (about 1.14–1.35 mmol/L) for ages 24 to 97, with no sex split. Other labs differ: Labcorp prints 4.5–5.6 mg/dL (about 1.12–1.40 mmol/L), ARUP prints 1.09–1.30 mmol/L (about 4.4–5.2 mg/dL), and the Merck Manual says the range is typically 4.7–5.2 mg/dL (1.17–1.30 mmol/L). The Merck Manual defines low ionized calcium as below 4.7 mg/dL (1.17 mmol/L) and high as above 5.2 mg/dL (1.30 mmol/L). In a large hospital study about half of the patients tested had ionized calcium below the reference interval (Baird 2009), so low results are common in hospital settings. Mayo has not established an interval for ages 98 and older. Use the range printed on your own report first.","sources":[{"title":"Calcium, Ionized, Serum (test ID CAI)","url":"https://schnecklab.testcatalog.org/show/CAI","publisher":"Mayo Clinic Laboratories (catalog copy hosted by Schneck Medical Center)"},{"title":"Calcium, Ionized (test 004804)","url":"https://www.labcorp.com/tests/004804/calcium-ionized","publisher":"Labcorp"},{"title":"Calcium, Ionized, Serum (test 0020135)","url":"https://ltd.aruplab.com/Tests/Pub/0020135","publisher":"ARUP Laboratories"},{"title":"Overview of Disorders of Calcium Concentration","url":"https://www.merckmanuals.com/professional/nephrology/electrolyte-disorders/overview-of-disorders-of-calcium-concentration","publisher":"Merck Manual Professional Version","year":2025},{"title":"Hypocalcemia","url":"https://www.merckmanuals.com/professional/nephrology/electrolyte-disorders/hypocalcemia","publisher":"Merck Manual Professional Version","year":2025},{"title":"Hypercalcemia","url":"https://www.merckmanuals.com/professional/nephrology/electrolyte-disorders/hypercalcemia","publisher":"Merck Manual Professional Version","year":2025},{"title":"Reducing routine ionized calcium measurement","url":"https://pubmed.ncbi.nlm.nih.gov/19168556/","publisher":"Clinical Chemistry","year":2009}]}],"review":{"status":"ai-verified","label":"AI-verified against cited sources. Awaiting expert review","lastReviewed":"2026-10-03"},"summary":"Ionized calcium is the free, active part of the calcium in your blood. It is checked when total calcium or protein levels make the usual test hard to read.","url":"https://bloodtesttracker.com/markers/calcium-ionized","notice":"Information, not medical advice. Ranges differ between labs, so the range on your own report is the one your result is judged against."}