What is the normal range for serum calcium levels?

From the Guidelines

A normal blood calcium level is considered to be between 8.6 and 10.3 mg/dL (2.15 to 2.57 mmol/L) for adults. This range is based on the most recent and highest quality study available, which is the K/DOQI clinical practice guidelines for bone metabolism and disease in chronic kidney disease 1. It's essential to note that calcium in the blood exists in three distinct fractions: protein-bound calcium, free (ionized) calcium, and calcium complexed with various anions.

• The free calcium, which ranges from 4.65 to 5.28 mg/dL (1.16 and 1.32 mmol/L), is the physiologically active form and is tightly regulated by the body.
• The body regulates calcium through the actions of parathyroid hormone (PTH), vitamin D, and calcitonin, as well as the kidney's ability to excrete or reabsorb calcium.
• Maintaining normal calcium levels is crucial for proper nerve function, muscle contraction, blood clotting, and bone health. When interpreting calcium results, it's also important to consider albumin levels, as low albumin can affect total calcium measurements without changing the physiologically important ionized calcium, and a correction of the measured serum levels of calcium should be made if plasma levels of albumin are low 1.

From the Research

Normal Blood Calcium Levels

• The normal blood calcium level is not explicitly stated in the provided studies, but we can infer the normal range from the information given about hypercalcemia and hypocalcemia.
• According to 2, mild hypercalcemia is defined as a total calcium level of less than 12 mg/dL (<3 mmol/L) or an ionized calcium level of 5.6 to 8.0 mg/dL (1.4-2 mmol/L).
• Severe hypercalcemia is defined as a total calcium level of 14 mg/dL or greater (>3.5 mmol/L) or an ionized calcium level of 10 mg/dL or greater (≥2.5 mmol/L).
• Therefore, we can assume that the normal blood calcium level is likely below 12 mg/dL (<3 mmol/L) for total calcium and below 5.6 mg/dL (1.4 mmol/L) for ionized calcium.
• Additionally, 3 mentions that measurement of ionized Ca+2 is the preferred way to ascertain the diagnosis of hypocalcemia and hypercalcemia, but it does not provide a specific normal range.

Calcium Metabolism and Homeostasis

• Calcium metabolism is linked to magnesium and phosphate metabolism, and Ca+2 homeostasis is dependent on intestinal absorption, bone turnover, and renal reabsorption 3.
• The hormonal regulators of these processes are the parathyroid hormone (PTH), calcitriol {1,25-dihydroxyvitamin D [1,25(OH)2D]}, and serum ionized Ca+2 3.
• Disorders of Ca+2 metabolism, such as hypercalcemia and hypocalcemia, can be caused by various factors, including genetic mutations, dietary deficiencies, and certain medical conditions 2, 4.