Corrected calcium

Corrected Calcium

Corrected calcium is a calculated value used to estimate the true serum calcium concentration in patients with abnormal levels of serum albumin. Since calcium in the blood is bound to proteins, primarily albumin, the total serum calcium concentration can be misleading in cases of hypoalbuminemia or hyperalbuminemia. Corrected calcium provides a more accurate reflection of the physiologically active calcium in the blood.

Physiology

Calcium is a vital mineral in the human body, playing crucial roles in bone health, muscle function, nerve transmission, and blood clotting. Approximately 40% of calcium in the blood is bound to proteins, mainly albumin, while the rest is either ionized or complexed with anions. Ionized calcium is the biologically active form that is tightly regulated by parathyroid hormone (PTH) and vitamin D.

Importance of Corrected Calcium

In clinical practice, measuring ionized calcium directly is ideal but not always feasible due to cost and availability. Therefore, total serum calcium is often measured, and corrected calcium is calculated to account for variations in albumin levels. This correction is particularly important in patients with conditions such as liver disease, nephrotic syndrome, or malnutrition, where albumin levels are frequently altered.

Calculation

The corrected calcium can be calculated using the following formula:

\[ \text{Corrected Calcium (mg/dL)} = \text{Measured Total Calcium (mg/dL)} + 0.8 \times (4.0 - \text{Serum Albumin (g/dL)}) \]

This formula assumes that the normal albumin level is 4.0 g/dL. The correction factor of 0.8 is an approximation and may vary slightly depending on the laboratory or clinical guidelines.

Clinical Implications

Corrected calcium is used to assess calcium status in patients with abnormal albumin levels. It helps in diagnosing and managing conditions such as hypocalcemia and hypercalcemia. For instance, a patient with low albumin and low total calcium might have normal ionized calcium levels, which would be reflected in a normal corrected calcium value.

Limitations

While corrected calcium is a useful tool, it is not without limitations. The correction formula is an approximation and may not be accurate in all clinical situations. Direct measurement of ionized calcium is preferred when precise calcium status is critical, such as in critically ill patients or those undergoing major surgery.

Also see

• Calcium metabolism
• Hypocalcemia
• Hypercalcemia
• Albumin
• Ionized calcium