From the Guidelines
The albumin-corrected calcium level for a calcium of 2.42 mmol/L with an albumin of 29 g/L is 2.62 mmol/L. This calculation is crucial because calcium in the blood exists in both protein-bound (primarily to albumin) and free ionized forms, with the latter being physiologically active. When albumin levels are low, as in this case (normal range typically 35-50 g/L), the total serum calcium measurement may appear falsely low despite normal free calcium levels. The correction formula commonly used is: Corrected calcium (mmol/L) = Measured calcium + 0.02 × (40 - albumin in g/L) 1. Applying this formula: 2.42 + 0.02 × (40 - 29) = 2.42 + 0.02 × 11 = 2.42 + 0.22 = 2.62 mmol/L. This corrected value is above the typical normal range (2.2-2.6 mmol/L), suggesting hypercalcemia that may require clinical attention. When interpreting calcium levels in patients with abnormal albumin, this correction is essential for accurate assessment of calcium status and appropriate clinical decision-making. Key points to consider include:
- The importance of correcting total calcium for albumin levels to accurately assess calcium status
- The use of the formula Corrected calcium (mmol/L) = Measured calcium + 0.02 × (40 - albumin in g/L) for this correction
- The potential for hypercalcemia when the corrected calcium level exceeds the normal range
- The need for clinical attention when hypercalcemia is suspected based on corrected calcium levels 1.
From the Research
Albumin-Corrected Calcium Calculation
To calculate the albumin-corrected calcium level, several formulas can be used, as discussed in various studies 2, 3, 4, 5, 6.
- The traditional formula, often referred to as Payne's formula, is: Corrected Ca = Total Ca + 0.020 or 0.025 (40 - albumin (g/L)) 3.
- Another formula, proposed in a study, is: [Calcium (revised)] = plasma calcium (mg/dl) + [(4- Albumin (g/d)L)]*(plasma calcium (mg/dl)*0.052)] 2.
- A new formula, considering the difference in albumin analysis methods, is: corrected Ca = total Ca + {4- (BCP+ 0.3)} 6.
- A formula specifically for very elderly hospitalized patients is: Ca(2+) (mmol/l) = 0.592 - 0.00449 protein (g/l) + 0.410 total calcium (mmol/l) 5.
Calculation for Given Values
Given a calcium level of 2.42 mmol/L and an albumin level of 29 g/L, we can calculate the albumin-corrected calcium level using one of the formulas.
- Using Payne's formula with 0.025: Corrected Ca = 2.42 + 0.025 (40 - 29) = 2.42 + 0.025 * 11 = 2.42 + 0.275 = 2.695 mmol/L.
- Using the formula from 2, first convert the values to mg/dl: calcium = 2.42 mmol/L * 40.08 = 97.0 mg/dl, albumin = 29 g/L * 10 = 290 mg/dl. Then, [Calcium (revised)] = 97 + [(4- 29/10)](970.052) = 97 + (-1.9)*(5.044) = 97 - 9.583 = 87.417 mg/dl. Convert back to mmol/L: 87.417 mg/dl / 40.08 = 2.18 mmol/L.
- The other formulas require specific conditions or measurements not provided in the question, so they cannot be directly applied.
Note that the choice of formula may depend on the specific clinical context and the methods used for measuring calcium and albumin 6.