Corrected Calcium Calculator

Understanding Calcium and Albumin

Serum calcium exists in three forms: ionized (free, active), albumin-bound (inactive), and bound to other anions like phosphate or citrate. About 45% is ionized, 40% is albumin-bound, and 15% is bound to other anions.

Only ionized calcium is biologically active, regulating muscle contraction, nerve transmission, blood clotting, and bone metabolism. The albumin-bound fraction serves as a reservoir. When ionized calcium drops, calcium unbinds from albumin to maintain balance.

Standard lab tests measure total calcium (ionized + bound). When albumin is low, total calcium appears low even if ionized calcium is normal. This creates false alarms for hypocalcemia. Correcting for albumin estimates what the total calcium would be if albumin were normal (4.0 g/dL).

Medical disclaimer: This calculator is for educational purposes only. Calcium disorders require comprehensive evaluation by a healthcare provider. Never diagnose or treat calcium abnormalities based solely on this calculator. Severe hypocalcemia and hypercalcemia are medical emergencies.

Hypocalcemia: Causes and Symptoms

Hypocalcemia (corrected calcium <8.5 mg/dL) impairs neuromuscular function. Mild hypocalcemia causes perioral numbness, tingling in fingers and toes, and muscle cramps. Severe hypocalcemia (<7.0 mg/dL) causes tetany, seizures, laryngospasm, and heart arrhythmias.

Hypoparathyroidism is a common cause, occurring after thyroid surgery when parathyroid glands are accidentally removed or damaged. Parathyroid hormone (PTH) normally raises calcium by increasing bone resorption, kidney reabsorption, and vitamin D activation.

Vitamin D deficiency impairs intestinal calcium absorption, causing hypocalcemia despite normal PTH. Chronic kidney disease reduces vitamin D activation and phosphate excretion, leading to secondary hyperparathyroidism and low calcium.

Acute pancreatitis causes calcium to deposit in necrotic pancreatic tissue, dropping serum levels. Hypomagnesemia (<1.5 mg/dL) impairs PTH secretion and action, making hypocalcemia refractory to calcium replacement until magnesium is corrected.

Hypercalcemia: Causes and Management

Hypercalcemia (corrected calcium >10.5 mg/dL) causes fatigue, weakness, constipation, nausea, confusion, and kidney stones. The mnemonic 'stones, bones, groans, and psychiatric overtones' captures classic symptoms.

Primary hyperparathyroidism is the most common outpatient cause, often from a benign parathyroid adenoma. PTH is elevated, calcium is high, and phosphate is low. Treatment is surgical removal of the overactive gland.

Malignancy is the most common inpatient cause. Tumors secrete PTH-related peptide (PTHrP) or release bone-destroying cytokines. Lung, breast, kidney, and multiple myeloma are typical. PTH is suppressed, distinguishing it from primary hyperparathyroidism.

Vitamin D toxicity from excessive supplementation or granulomatous diseases like sarcoidosis raises calcium by increasing intestinal absorption. Thiazide diuretics, immobilization, and familial hypocalciuric hypercalcemia are other causes. Severe hypercalcemia (>14 mg/dL) is a medical emergency requiring IV fluids, bisphosphonates, and sometimes dialysis.