Calcium (Total)
Calcium drives nerve transmission, muscle contraction, blood clotting and bone strength. Levels are tightly regulated; deviations always have a cause worth chasing.
What it measures
Roughly 99% of body calcium is in bone; the 1% in blood does the second-by-second physiological work. About half of blood calcium is bound to albumin, so a low albumin level can drop total calcium without actually lowering the active ionised calcium — which is why some labs report a corrected calcium that accounts for albumin. PTH, vitamin D and calcitonin keep the level in a narrow band.
What a high value can mean
- Primary hyperparathyroidism — the most common cause of unexpected hypercalcaemia in outpatients; PTH inappropriately normal or high.
- Malignancy — bone metastases, multiple myeloma, paraneoplastic PTH-related peptide.
- Vitamin D toxicity — supplementation without monitoring.
- Sarcoidosis, granulomatous diseases — extra-renal vitamin D activation.
- Thiazide diuretics, lithium — drug-induced.
What a low value can mean
- Vitamin D deficiency — the dominant outpatient cause.
- Hypoparathyroidism — post-surgical (after neck surgery), autoimmune.
- Chronic kidney disease — phosphate retention plus impaired vitamin D activation.
- Acute pancreatitis — calcium saponification.
- Hypomagnesaemia — calcium correction needs magnesium replacement first.
When to discuss with a doctor
Total calcium outside 8.5–10.5 mg/dL warrants a primary-care visit. Hypercalcaemia >12 mg/dL with symptoms (lethargy, confusion, polyuria) needs urgent evaluation. Severe hypocalcaemia (<7) with tetany is an emergency. Mediora.AI flags critical values and pairs calcium with vitamin D and PTH when those values are available.