Last updated October 10, 2026 · Report an error
Corrected Calcium, the standard published correction formula for low serum albumin (Payne RB et al., "Interpretation of serum calcium in patients with abnormal serum proteins", British Medical Journal, 1973): Corrected Ca (mg/dL) = Measured Ca + 0.8 x (4 - Serum Albumin (g/dL)). About 40-45% of serum calcium is protein-bound (mostly to albumin), so low albumin can make total calcium appear falsely low; this formula estimates what total calcium would be at a normal albumin of 4 g/dL. For general reference and educational purposes only — not a medical diagnosis. Consult a doctor for actual calcium assessment (ionized calcium, when available, is more direct).
How it works
Enter measured total calcium in mg/dL and serum albumin in g/dL. The tool applies the standard Payne correction formula.
- Enter measured total calcium (mg/dL).
- Enter serum albumin (g/dL).
- Click Calculate to see your results.
Examples
Measured Ca 8.0 mg/dL, Albumin 2.0 g/dL
Corrected Ca = 8.0 + 0.8 x (4 - 2.0) = 8.0 + 1.6 = 9.6 mg/dL.
Who should use it
- Reviewing a calcium lab result in a patient with low albumin.
- Nephrology, endocrinology, and critical care education.
Industry applications
- Nephrology and endocrinology reference
- Critical care and hospital medicine education
Advantages
- Long-established, widely cited, standard correction formula.
- Simple to apply with two routinely available lab values.
Limitations
- An estimate — ionized calcium, when available, is the more direct measurement.
- Less validated at extreme albumin levels.
Common mistakes to avoid
- Using an outdated albumin value from a different lab draw than the calcium measurement.
- Assuming the correction applies equally well at very extreme albumin levels, where the linear formula is less validated.
Best practices
- Use calcium and albumin values drawn from the same blood sample for the most meaningful correction.
Tips
- When available and clinically indicated, an ionized calcium measurement avoids the need for albumin correction altogether.