Albumin-Corrected Calcium Calculator

Calcium circulates in three forms: about 50% as free ionised calcium, about 40% bound to protein (mostly albumin), and about 10% complexed with anions such as citrate and phosphate. Only the ionised fraction is physiologically active — it is what drives nerve conduction, muscle contraction, and clotting.

A routine chemistry panel reports total calcium, which sums all three. If albumin falls — in liver disease, nephrotic syndrome, malnutrition, or any acute illness — the protein-bound fraction falls with it and the total drops, while the ionised fraction may be entirely normal. Read without context, that looks like hypocalcaemia that is not there.

The Payne correction estimates what the total calcium would have been at a normal albumin of 4.0 g/dL. Each 1 g/dL that albumin sits below 4.0 adds 0.8 mg/dL to the reported calcium. The same slope works in reverse when albumin is high.

1. 1.Subtract the measured albumin from 4.0 g/dL (or from 40 g/L in SI units).
2. 2.Multiply that difference by 0.8 (or by 0.02 in SI units).
3. 3.Add the result to the measured total calcium.

A measured calcium of 8.4 mg/dL with an albumin of 3.0 g/dL: the albumin deficit is 1.0, multiplied by 0.8 gives 0.8, and the corrected calcium is 9.2 mg/dL — normal, where the raw value looked low. In SI, 2.10 mmol/L with an albumin of 30 g/L gives 2.10 + 0.02 × 10 = 2.30 mmol/L.

The correction runs downward too. A calcium of 10.4 mg/dL with an albumin of 4.6 g/dL corrects to 9.9 mg/dL: what read as borderline high is normal once the raised albumin is accounted for. Dehydration with haemoconcentration is the usual reason for that pattern.

Reference intervals vary slightly between laboratories, typically by around 0.2 mg/dL at each end, so always compare against the range printed on your own report rather than a generic one.

Severity matters as much as the category. Hypercalcaemia above roughly 12 mg/dL usually causes symptoms — thirst, polyuria, constipation, confusion — and above 14 mg/dL is a medical emergency. Hypocalcaemia below about 7 mg/dL can cause tetany, laryngospasm, and seizures. Rate of change matters too: a calcium that has moved quickly causes symptoms at levels a slowly adapted patient tolerates.

It is a regression line from a single hospital population in 1973, and it has been repeatedly shown to agree poorly with directly measured ionised calcium. The correction assumes albumin is the only variable that matters, and that its binding relationship is fixed. Neither holds reliably.

• Binding depends on pH. Alkalosis increases albumin binding and lowers ionised calcium; acidosis does the reverse. The formula has no pH term.
• In chronic kidney disease, adjusted calcium misclassifies calcium status often enough that it is a recognised clinical problem, particularly in stage 5 and on dialysis.
• In critical illness, inflammation, and severe hypoalbuminaemia — the exact situations that prompt correcting — the formula performs at its worst.
• Multiple studies find adjusted calcium is no better than unadjusted total calcium at predicting ionised calcium, tending to underestimate true hypocalcaemia and overestimate true hypercalcaemia.

In May 2026 a joint working group of the International Osteoporosis Foundation, the IFCC Committee on Bone Metabolism, and the EFLM Committee on CKD published a position statement recommending that laboratories stop routinely reporting albumin-adjusted calcium at all, and order ionised calcium where calcium status genuinely matters.

A genuinely abnormal corrected calcium is a finding to explain, not a result to repeat until it normalises.

The usual next steps for a confirmed high calcium are parathyroid hormone, phosphate, magnesium, vitamin D, and kidney function — PTH in particular separates hyperparathyroidism from almost everything else in a single test.