Calcium-Phosphate Product Calculator
Calculate the calcium-phosphate product from serum calcium and phosphate, a monitoring parameter in chronic kidney disease and mineral bone disorder management.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| Calcium-Phosphate Product Calculator | — | Ca × P product = corrected calcium × phosphate | mg²/dL² |
Step-by-Step Examples
Calcium 9.5, phosphate 4.0, albumin 4.0 g/dL.
- Albumin normal, so corrected calcium = 9.5
- Product = 9.5 × 4.0
- Product = 38 mg²/dL²
Calcium 8.2, phosphate 5.5, albumin 2.6 g/dL.
- Corrected calcium = 8.2 + 0.8 × (4.0 − 2.6) = 9.32
- Product = 9.32 × 5.5
- Product = 51.3 mg²/dL²
- Uncorrected, the product would have read 45.1 and understated the value
Calcium 10.4, phosphate 7.2, albumin 4.0 g/dL.
- Corrected calcium = 10.4
- Product = 10.4 × 7.2
- Product = 74.9 mg²/dL²
Real-World Applications
Common Mistakes to Avoid
Roughly 40% of serum calcium is albumin-bound. In hypoalbuminaemia — common in kidney disease — uncorrected total calcium substantially understates the physiologically active fraction.
KDIGO guidance has moved away from the calcium-phosphate product toward managing calcium and phosphate individually, since the product can conceal opposing abnormalities.
When albumin is very low or acid-base status is abnormal, corrected calcium formulas perform poorly, and direct ionised calcium measurement is more reliable.