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Electrolytes
Calcium (total)
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This is the date the draft was written, not a medical review date.
Total calcium includes protein-bound (mostly albumin), complexed and ionised fractions. The physiologically active ionised fraction is about half of the total.
Reference interval
| Conventional (mg/dL) | SI (mmol/L) | |
|---|---|---|
| Adults | 8.5–10.5 mg/dL | 2.12–2.62 mmol/L |
Specimen: Serum · Conventional × 0.2495 = SI
Causes of high values
Primary hyperparathyroidism and malignancy (the two commonest causes), vitamin D excess, granulomatous disease, thiazides, lithium, immobilisation and milk-alkali syndrome.
Causes of low values
Hypoparathyroidism, vitamin D deficiency, chronic kidney disease, hypomagnesaemia, acute pancreatitis, hypoalbuminaemia (total only) and drugs such as loop diuretics and bisphosphonates.
Pre-analytical and method notes
Total calcium must be interpreted with albumin (corrected calcium) or, preferably, measured ionised calcium in critical illness, acid-base disturbance or abnormal proteins. Reference limits vary by laboratory (commonly 2.15-2.55 mmol/L, 8.6-10.2 mg/dL). 1 mmol/L equals about 4.0 mg/dL.
Related calculators
References
- Rifai N, Horvath AR, Wittwer CT. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier, 6th edition (2018) — Tier 3 (textbook)
- Loscalzo J, et al.. Harrison's Principles of Internal Medicine. McGraw-Hill, 21st edition (2022) — Tier 3 (textbook)
- Williams Textbook of Endocrinology. Elsevier, 14th edition (2019) — Tier 3 (textbook)
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