Corrected Calcium Calculator
Adjust a total serum calcium reading for a low or high albumin level, so hypo- and hypercalcaemia are not masked by protein binding.
How it works
Corrected Ca (mg/dL) = measured Ca + 0.8 × (reference albumin − measured albumin) · reference albumin usually 4.0 g/dL
About 40% of serum calcium is bound to albumin, so a low albumin level lowers the total calcium a lab reports even when the physiologically active ionised calcium is normal. The correction adds back roughly 0.8 mg/dL of calcium for every 1 g/dL that albumin sits below the reference, unmasking true hypocalcaemia or hypercalcaemia. The formula is a rule of thumb — it is least reliable at extreme albumin levels, and a directly measured ionised calcium is preferred when accuracy is critical.
Worked example
A patient has total calcium 8.4 mg/dL with albumin 3.0 g/dL against a 4.0 g/dL reference. Corrected calcium = 8.4 + 0.8 × (4.0 − 3.0) = 8.4 + 0.8 = 9.2 mg/dL, which is within the normal range despite the low measured value.
Sources: Albumin-corrected calcium
Frequently asked questions
Why correct calcium for albumin?
Total calcium includes the fraction bound to albumin. When albumin is low, total calcium reads low even if the active ionised calcium is normal — the correction restores a truer picture and prevents over-treating a false hypocalcaemia.
Is corrected calcium as good as ionised calcium?
No. A directly measured ionised calcium is the gold standard, especially in critical illness or abnormal pH. The albumin correction is a convenient estimate that can be inaccurate at very low or high albumin.
What is a normal corrected calcium?
Most laboratories use roughly 8.5–10.5 mg/dL (about 2.1–2.6 mmol/L) as the normal total calcium range, though exact cut-offs vary by lab.
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Educational estimate using standard published formulas — not medical advice, a diagnosis, or a substitute for clinical judgement. Dosing, diagnosis and treatment must be decided by a qualified clinician using validated tools and the full clinical picture.