Blood calcium

Blood Calcium

Blood calcium, also known as serum calcium, is a critical component of the human body's physiological processes. It plays a vital role in various bodily functions, including bone health, muscle contraction, nerve signaling, and blood clotting. The regulation of blood calcium levels is tightly controlled by the body to ensure proper functioning of these processes.

Physiology

Calcium is the most abundant mineral in the human body, with about 99% stored in the bones and teeth, and the remaining 1% circulating in the blood and other tissues. Blood calcium exists in three forms:

• Ionized calcium: This is the biologically active form of calcium, accounting for about 50% of the total calcium in the blood.
• Protein-bound calcium: Approximately 40% of blood calcium is bound to proteins, primarily albumin.
• Complexed calcium: The remaining 10% is complexed with anions such as phosphate and citrate.

The normal range for total blood calcium is typically between 8.5 and 10.5 mg/dL, although this can vary slightly depending on the laboratory and measurement methods.

Regulation

The regulation of blood calcium levels involves several hormones and organs:

• Parathyroid hormone (PTH): Secreted by the parathyroid glands, PTH increases blood calcium levels by stimulating osteoclasts to break down bone, increasing renal tubular reabsorption of calcium, and promoting the activation of vitamin D.
• Calcitonin: Produced by the parafollicular cells of the thyroid gland, calcitonin lowers blood calcium levels by inhibiting osteoclast activity and increasing calcium excretion by the kidneys.
• Vitamin D: In its active form, calcitriol, vitamin D enhances intestinal absorption of calcium and phosphate, contributing to the maintenance of blood calcium levels.

Clinical Significance

Abnormal blood calcium levels can lead to various health issues:

• Hypercalcemia: Elevated blood calcium levels can result from hyperparathyroidism, malignancies, excessive vitamin D intake, or other conditions. Symptoms may include nausea, vomiting, constipation, polyuria, and neurological disturbances.
• Hypocalcemia: Low blood calcium levels can be caused by hypoparathyroidism, vitamin D deficiency, renal disease, or other factors. Symptoms may include muscle cramps, tetany, seizures, and cardiac arrhythmias.

Diagnostic Evaluation

Blood calcium levels are typically measured as part of a comprehensive metabolic panel. Both total calcium and ionized calcium can be measured, with ionized calcium providing a more accurate assessment of the physiologically active calcium.

Treatment

Treatment of abnormal blood calcium levels depends on the underlying cause:

• Hypercalcemia: Treatment may involve hydration, diuretics, bisphosphonates, calcitonin, or surgery in cases of hyperparathyroidism.
• Hypocalcemia: Treatment may include calcium supplements, vitamin D analogs, and addressing the underlying cause.

Also see

• Calcium metabolism
• Parathyroid hormone
• Vitamin D
• Hypercalcemia
• Hypocalcemia