Normal Calcium Levels — Reference Ranges by Age and Test Type
Understand normal calcium levels for total serum calcium, ionized calcium, and urine calcium across all age groups. Includes causes of high and low results. Free calculator.
Normal Calcium Reference Ranges
Calcium reference ranges differ based on measurement type (total vs. ionized), specimen type (serum vs. urine), and patient age. Understanding which reference range applies to your result is essential for correct interpretation.
| Test | Normal Range (US) | Normal Range (SI) | Notes |
|---|---|---|---|
| Total serum calcium (adults) | 8.5–10.5 mg/dL | 2.12–2.62 mmol/L | Includes protein-bound fraction |
| Ionized calcium (adults) | 4.5–5.3 mg/dL | 1.12–1.32 mmol/L | Active physiologic fraction |
| Total calcium (newborns) | 7.6–10.4 mg/dL | 1.90–2.60 mmol/L | Lower normal threshold |
| Total calcium (children) | 8.8–10.8 mg/dL | 2.20–2.70 mmol/L | Slightly higher upper limit |
| 24-hour urine calcium | 100–300 mg/24h | 2.5–7.5 mmol/24h | Varies with dietary intake |
Symptoms by Calcium Level
Mild hypocalcemia (7.5–8.5 mg/dL) is often asymptomatic. Moderate hypocalcemia (7.0–7.5 mg/dL) can cause muscle cramps, perioral tingling, and Trousseau's/Chvostek's signs. Severe hypocalcemia (<7.0 mg/dL) can cause tetany, laryngospasm, and seizures requiring emergency treatment. Hypercalcemia (>10.5 mg/dL) causes symptoms classically remembered as "bones, stones, groans, and psychic moans" — bone pain, kidney stones, constipation, and mood changes.
Frequently Asked Questions
What is a dangerously low calcium level?
Total serum calcium below 7.0 mg/dL (1.75 mmol/L) is considered severely low and can cause tetany, seizures, and life-threatening laryngospasm. Emergency IV calcium supplementation is typically required at these levels. Ionized calcium below 0.7 mmol/L requires urgent intervention.
Does calcium level change throughout the day?
Yes, modestly. Total serum calcium is slightly higher in the morning and lower in the afternoon, with diurnal variation of about 0.3 mg/dL. It is also influenced by body position — values drawn lying flat can be up to 0.5 mg/dL lower than those drawn sitting upright, due to albumin redistribution.