Calcium Correction for Hypoalbuminemia

What this tool does

It applies the widely taught Payne adjustment to total serum calcium when albumin is abnormal, to approximate calcium at a reference albumin level.

Formula

Ca_corrected = Ca_measured + 0.8 × (4.0 − albumin) [mg/dL, g/dL]

Some references use 0.2 × (40 − albumin g/L) in SI form; mathematically related when converted consistently.

References

Payne RB, et al. Interpretation of serum calcium in patients with abnormal serum proteins. Br Med J. 1973;4(5893):643-646.

Limitations

• Does not replace ionized calcium in critical illness, renal failure, paraproteinemia, or chelation states.
• Hyperalbuminemia and globulin-bound calcium shifts are not fully captured.

Interpretation & next steps (teaching)

• When albumin is low or calcium is borderline, ionized calcium measurement may clarify true physiologic status.
• Parathyroid, vitamin D, renal function, and magnesium interact with calcium—interpret corrected values in that context.
• Therapy thresholds (replacement, cinacalcet, etc.) follow guidelines and specialist input—not this estimate alone.

Ionized calcium or direct measurement is preferred when clinically indicated; this is an estimate.