Corrected Calcium Calculator
Calculate albumin-corrected serum calcium using the standard correction formula (mg/dL). Used to identify true hypercalcaemia or hypocalcaemia when albumin is abnormal.
How to use this tool
- Enter measured serum calcium and serum albumin in the fields above.
- Results update instantly as you type — or click Calculate.
- Read your corrected calcium and the full breakdown beneath it.
Educational estimate — not medical advice. Consult a clinician.
About 40% of serum calcium is bound to albumin. When albumin is low, total calcium appears falsely low. The correction: Corrected Ca = Measured Ca + 0.8 × (4.0 − Albumin) adjusts for this. Ionised calcium measurement is the gold standard.
Formula
Corrected calcium (mg/dL) = Measured calcium + 0.8 × (4.0 − Albumin)
Where albumin is in g/dL and the normal reference albumin is 4.0 g/dL.
How it works
Approximately 40% of serum calcium is bound to albumin, so total calcium readings fall or rise with albumin levels even when ionised (free) calcium is unchanged. This calculator applies the Payne correction formula, which adds 0.8 mg/dL for each 1 g/dL that albumin falls below the reference value of 4.0 g/dL. The formula assumes a linear relationship between albumin and calcium binding and a normal reference albumin of 4.0 g/dL; it provides a useful screening estimate but may be less accurate in critically ill patients, where ionised calcium measurement is preferred.
Worked example
Worked example
- Inputs: measured serum calcium = 9.0 mg/dL, serum albumin = 3.0 g/dL.
- Albumin deficit = 4.0 − 3.0 = 1.0 g/dL.
- Correction = 0.8 × 1.0 = 0.8 mg/dL.
- Corrected calcium = 9.0 + 0.8 = 9.8 mg/dL.
Corrected calcium = 9.8 mg/dL — Normal range (8.5–10.2 mg/dL).
Key terms
- Total serum calcium
- The combined concentration of protein-bound, complexed, and ionised (free) calcium measured in blood, expressed in mg/dL.
- Albumin
- The most abundant plasma protein; its level determines how much calcium is protein-bound and therefore affects total calcium readings.
- Ionised calcium
- The biologically active, unbound fraction of calcium in blood; the gold standard for assessing true calcium status, especially in critical illness.
- Hypocalcaemia
- A state of abnormally low calcium activity, defined by a corrected calcium below 8.5 mg/dL; symptoms include muscle cramps and tetany.
- Hypercalcaemia
- A state of abnormally high calcium, defined by a corrected calcium above 10.2 mg/dL; causes include hyperparathyroidism and malignancy.
Frequently asked questions
- When do I need a corrected calcium?
- Whenever serum albumin is outside the normal range (roughly 3.5–5.0 g/dL). In patients with malnutrition, liver disease, or nephrotic syndrome albumin is often low, making total calcium misleadingly low.
- What is the normal serum calcium range?
- Most labs use 8.5–10.2 mg/dL (2.12–2.55 mmol/L) as the adult normal range, though ranges vary slightly between laboratories.
- Is this formula always accurate?
- The Payne/correction formula has known limitations and can over- or under-correct. Ionised calcium measurement avoids the need for correction entirely and is preferred when accuracy is critical.