Calcium (Ca) — Normal Range & Interpretation

Clinical Context

Serum calcium reflects total circulating calcium, including protein-bound and ionized fractions. Calcium drives neuromuscular excitability, cardiac contractility, coagulation, and bone mineralization. Parathyroid hormone and vitamin D tightly regulate levels, so abnormal calcium often signals endocrine, renal, or malignant pathology. Because roughly half of calcium binds albumin, NPs correct total calcium in patients with hypoalbuminemia to avoid misclassifying true calcium status.

Hypercalcemia most often results from primary hyperparathyroidism in outpatients and malignancy in hospitalized patients. Thiazide diuretics, lithium, vitamin D toxicity, sarcoidosis, and prolonged immobilization also elevate calcium. Hypocalcemia stems from hypoparathyroidism, vitamin D deficiency, chronic kidney disease, hypomagnesemia, acute pancreatitis, and post-thyroidectomy states. Symptoms track severity: hypercalcemia produces stones, bones, abdominal groans, and psychiatric overtones, while hypocalcemia triggers perioral numbness, tetany, Chvostek sign, Trousseau sign, and QT prolongation.

Classic AANP vignette: the textbook presentations that link calcium abnormalities to underlying etiology. Expect questions pairing hypercalcemia with hyperparathyroidism or malignancy and hypocalcemia with post-thyroidectomy tetany or vitamin D deficiency. Know the albumin correction concept, the association between magnesium and calcium regulation, and the ECG findings that accompany each derangement. Recognize when calcium changes demand urgent referral versus outpatient workup with PTH and vitamin D levels.

Practice Questions

Related Labs

• Sodium (Na) — mEq/L
• Potassium (K) — mEq/L
• Chloride (Cl) — mEq/L
• CO2 (Bicarbonate) — mEq/L
• BUN — mg/dL

Sources

• MedlinePlus