Plasma calcium concentration

Plasma calcium refers to the concentration of free and bound forms of the element calcium in blood plasma. About half exists as free ionized Ca²⁺—the biologically active form—while the rest is bound mainly to albumin or complexed with anions like phosphate. Plasma levels are tightly regulated within narrow limits (~2.2–2.6 mmol/L total; ~1.3–1.5 mmol/L ionized) because even small deviations can disrupt neuromuscular function and other vital processes. Regulation occurs through interplay between: * The parathyroid glands—which secrete parathyroid hormone in response to low plasma Ca²⁺, * The thyroid gland’s parafollicular cells—which secrete calcitonin when levels are high, * The kidneys—which filter/reabsorb/excrete Ca²⁺, * The intestines—where vitamin D increases dietary absorption, * And bones—which serve as both source and sink for rapid adjustments. Disorders affecting any part of this system can result in abnormal plasma concentrations with significant clinical consequences such as tetany from hypocalcemia or cardiac arrhythmia from hypercalcemia. "An important aspect of calcium metabolism is plasma calcium homeostasis...The level...is regulated by hormones parathyroid hormone...and calcitonin." In summary: Plasma calcium itself is not a druggable target but rather an essential physiological variable controlled by multiple molecular targets—including receptors like the parathyroid hormone receptor—and serves as both a biomarker for disease states and an endpoint for therapeutic intervention.

Other names

Blood calciumserum calciumplasma Ca²⁺

Drugs may increase or decrease intestinal absorption of Ca²⁺ (vitamin D analogs), alter bone resorption/deposition (bisphosphonates, PTH analogs), or modify renal reabsorption/excretion of Ca²⁺. Some drugs act on the parathyroid gland via the CaSR to modulate PTH release. Calcitonin lowers blood Ca²⁺ by inhibiting osteoclast-mediated bone resorption. Thiazide diuretics reduce urinary excretion; loop diuretics increase it.