What It Measures
A serum calcium test measures the total amount of calcium circulating in the blood, including both the protein-bound fraction (about 40%, mostly bound to albumin) and the free ionized (active) fraction. It reflects the body's ability to maintain calcium homeostasis through the interplay of parathyroid hormone, vitamin D, kidneys, and bone.
Calcium is the most abundant mineral in the body, essential for bone health, muscle contraction, nerve signaling, and blood clotting. Serum calcium levels reflect the balance between dietary intake, bone metabolism, and hormonal regulation (primarily parathyroid hormone and vitamin D), making it a critical marker for metabolic, bone, and endocrine health.
Current Value
What High Means
Elevated calcium (hypercalcemia) most commonly indicates primary hyperparathyroidism (overactive parathyroid glands) or malignancy (cancer producing PTHrP). Other causes include excessive vitamin D supplementation, granulomatous diseases (sarcoidosis), thyrotoxicosis, prolonged immobilization, thiazide diuretics, and milk-alkali syndrome. Chronic hypercalcemia increases risk of kidney stones, renal insufficiency, cardiac arrhythmias, and cognitive impairment.
Possible Symptoms
Fatigue, weakness, nausea, vomiting, constipation, excessive thirst, frequent urination, bone pain, kidney stones, confusion, depression, cognitive impairment, cardiac arrhythmias, abdominal pain
What Low Means
Low calcium (hypocalcemia) can result from vitamin D deficiency, hypoparathyroidism (often post-surgical), chronic kidney disease (impaired vitamin D activation), magnesium deficiency (impairs PTH secretion), malabsorption syndromes (celiac disease, pancreatitis), or medications (bisphosphonates, loop diuretics). Severe hypocalcemia can cause neuromuscular irritability, tetany, seizures, and cardiac dysfunction.
Possible Symptoms
Muscle cramps and spasms, numbness and tingling (perioral, fingers, toes), tetany, seizures, fatigue, brittle nails, dry skin, anxiety, depression, confusion, heart palpitations, difficulty swallowing (laryngospasm)
Risk Factors
Osteoporosis, kidney stones, chronic kidney disease, hyperparathyroidism, hypoparathyroidism, cardiac arrhythmias, malignancy, pancreatitis, neuromuscular disorders, vitamin D deficiency, malabsorption syndromes
Actionable Advice
Supplements
- •Calcium citrate
- •Calcium carbonate
- •Vitamin D3
- •Magnesium glycinate
- •Vitamin K2 (MK-7)
- •Boron
Diet & Lifestyle
- •Consume calcium-rich foods daily (dairy, sardines, leafy greens, fortified foods)
- •Ensure adequate vitamin D through sun exposure (15-20 min/day) or supplementation
- •Include weight-bearing and resistance exercise to support bone calcium retention
- •Maintain adequate magnesium intake (nuts, seeds, dark chocolate) as it regulates calcium metabolism
- •Limit excessive caffeine and sodium which increase urinary calcium loss
- •Avoid excessive alcohol which impairs calcium absorption
- •Space calcium supplements away from iron and thyroid medications to avoid absorption interference
- •Get vitamin K2 from fermented foods (natto, aged cheese) to direct calcium to bones rather than arteries
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Historical Trend
Related Biomarkers
Resources & Studies
All Readings
| Date | Value | Change |
|---|---|---|
| 2026-01-28 | 9.1 mg/dL | -0.3 |
| 2025-08-25 | 9.4 mg/dL | +0.4 |
| 2025-06-27 | 9 mg/dL | — |