Corrected Calcium Calculator

It is unreliable. Multiple studies — Law 2021 in Nephrology and the Nature Scientific Reports 2020 analysis among others — have shown that the Payne-corrected calcium agrees with the directly-measured ionised calcium in only about 40% of stage 5 CKD and dialysis patients. In that population the corrected value can over-estimate or under-estimate the ionised fraction, and the direction of the error is patient-specific. For clinical decisions in CKD or on dialysis, a direct ionised calcium measurement is preferred where the lab provides it.

Most UAE laboratories report total calcium in mmol/L and serum albumin in g/L — the SI convention also used across the EU and much of Asia. US laboratories typically report calcium in mg/dL and albumin in g/dL. This calculator converts between both internally; the user only needs to set the unit toggle to match the report in front of them.

When albumin is within the normal range (around 35–50 g/L or 3.5–5.0 g/dL), the Payne correction barely moves the value — usually by less than 0.05 mmol/L. The uncorrected total calcium is generally sufficient for clinical interpretation. The correction matters most when albumin is below about 35 g/L (3.5 g/dL), where a measured low total calcium may simply reflect the low albumin rather than a true calcium disturbance.

Direct ionised calcium is preferred whenever the Payne correction is known to be unreliable or when the clinical stakes are high. The standard list includes: chronic kidney disease (any stage), dialysis or end-stage renal disease, severe hypoalbuminaemia (typically albumin below 30 g/L), critical illness or sepsis, multiple transfusions of citrated blood, significant acid–base disturbance (the ionised fraction shifts with pH), and any borderline result where the clinical decision would change based on the calcium value.