serumkalcium

Serum calcium refers to the concentration of calcium in the blood serum. It exists in two main forms: ionized (free) calcium, which is biologically active, and calcium bound to proteins (primarily albumin) or complexed with anions. The total serum calcium value represents the sum of ionized and bound calcium. Normal ranges vary by laboratory, but typical adult values are about 8.8–10.4 mg/dL (2.20–2.60 mmol/L) for total calcium, with ionized calcium around 4.5–5.3 mg/dL (1.12–1.32 mmol/L).

Calcium homeostasis is tightly regulated by the joints of the parathyroid hormone, active vitamin D (calcitriol), and calcitonin. Parathyroid hormone increases serum calcium through bone resorption, renal reabsorption, and intestinal absorption; calcitonin lowers calcium levels; vitamin D promotes intestinal calcium uptake. Serum calcium can be influenced by acid–base status and by serum albumin, which affects total calcium measurements.

Measurement and interpretation considerations include the use of corrected calcium to account for hypo- or hyperalbuminemia: corrected calcium = measured calcium plus 0.8 × (4 − albumin in g/dL). Ionized calcium measurements are more physiologically informative when albumin levels or pH are abnormal, or in critical care or neonates. Preanalytical factors such as sample type, temperature, and handling can affect results; ionized calcium requires careful sample handling and direct measurement.

Clinical relevance of serum calcium spans screening and management of endocrine or metabolic disorders, assessment of bone and mineral metabolism, and monitoring in conditions such as chronic kidney disease, malnutrition, or after certain medications. Abnormal levels prompt evaluation for parathyroid disorders, vitamin D deficiency, malignancy, kidney disease, or medications affecting calcium balance.