Serum Calcium
Also known as: Total calcium, Serum Ca, Corrected calcium, Ionised calcium
Calcium is tightly regulated by PTH, vitamin D, and calcitonin. Abnormal calcium — whether high or low — can cause symptoms ranging from muscle cramps to kidney stones to cardiac arrhythmias.
Venous blood (serum separator tube — no tourniquet excess)
2–4 hours
Not required
Metabolic Panel
Reference Ranges
| Measurement | Reference Range | Unit |
|---|---|---|
| Total calcium | 8.6 – 10.3 | mg/dL |
| Ionised calcium | 4.6 – 5.3 | mg/dL |
Reference ranges are typical adult values. Your laboratory may use slightly different intervals — always use your lab's reported reference.
What This Test Measures
Total serum calcium has two fractions: about 45% is ionised (free, biologically active), 40% is protein-bound (mainly to albumin), and 15% is complexed to anions. Only ionised calcium is physiologically active. When albumin is low, total calcium falls without any change in ionised calcium — hence the need for albumin correction. Ionised calcium can be measured directly (ionised calcium test, requires prompt processing).
When Is This Test Ordered?
- Hypercalcaemia symptoms: fatigue, constipation, kidney stones, confusion, polyuria
- Hypocalcaemia symptoms: muscle cramps, tingling, Chvostek's sign, tetany
- Parathyroid disease investigation
- Bone disease and vitamin D deficiency workup
- Malignancy monitoring (bony metastases, PTHrP-secreting tumours)
- Part of routine metabolic panel
When Results Are High
Hypercalcaemia (above 10.5 mg/dL) is caused by primary hyperparathyroidism or malignancy in 90% of cases. Malignancy causes rapid, severe hypercalcaemia; hyperparathyroidism causes chronic, mild elevation often found incidentally. Above 14 mg/dL is a hypercalcaemic crisis requiring emergency treatment.
When Results Are Low
Hypocalcaemia (below 8.6 mg/dL, or corrected for albumin) causes neuromuscular excitability — tingling, tetany, Chvostek's sign (facial twitch on tapping). Causes: hypoparathyroidism (post-thyroid surgery), vitamin D deficiency, chronic kidney disease, hypomagnesaemia.
Factors That Can Affect Your Result
- Always correct for albumin: corrected Ca = measured Ca + 0.8 × (4 – albumin)
- Prolonged tourniquet and fist clenching raise ionised calcium through local acidosis
- Ionised calcium must be processed within 15 minutes (pH-sensitive)
- PTH drives calcium up; vitamin D drives intestinal absorption; calcitonin drives it down
Tracking This Test Over Time
A mildly elevated calcium (10.5–11.5 mg/dL) found incidentally is most likely primary hyperparathyroidism — confirm with a simultaneous PTH, which will be inappropriately elevated. Most cases are caused by a single benign adenoma and are curable by surgery.
Track your Calcium in LoomsRelated Tests
Vitamin D
Vitamin D deficiency affects an estimated 1 billion people worldwide and is particularly prevalent in the Middle East, where sun exposure is paradoxically limited by indoor lifestyles and clothing. This test measures your actual stored vitamin D level.
Albumin
Albumin is the most abundant plasma protein, made exclusively by the liver. It maintains oncotic pressure (keeping fluid in blood vessels) and transports hormones, drugs, and fatty acids. Low albumin is one of medicine's most informative and under-appreciated findings.
Uric Acid
Uric acid is the end product of purine metabolism. Elevated levels (hyperuricaemia) are the underlying cause of gout and are associated with kidney stone formation, hypertension, and metabolic syndrome.
Medical disclaimer
This page is for educational purposes only and does not constitute medical advice. Reference ranges vary between laboratories, and results must be interpreted in the context of your symptoms, history, and other tests. Always discuss your results with your healthcare provider. Content reviewed by the Looms medical team, 2026-06-01.