🦴 Corrected Calcium Calculator Payne Formula
Compute albumin-corrected serum calcium to unmask hidden hypo- or hypercalcemia in patients with hypoalbuminemia.
ℹ️ For educational and reference use only. Does not replace professional medical diagnosis or treatment.
Units: mg/dL (normal 8.5–10.5)
Units: g/dL (normal 3.5–5.0)
📊 Results
📋 Calcium Reference Ranges
| Category | Corrected Ca (mg/dL) | Interpretation | Common Causes |
|---|---|---|---|
| Hypocalcemia | < 8.5 | Low calcium | Hypoparathyroidism, vitamin D deficiency, CKD, magnesium depletion |
| Normal | 8.5 – 10.5 | Within reference | — |
| Hypercalcemia | > 10.5 | High calcium | Primary hyperparathyroidism, malignancy, vitamin D toxicity, sarcoidosis |
🔍 When is Correction Most Important?
🫁 Cirrhosis
Hepatic synthetic failure reduces albumin. Total calcium appears low while ionized calcium may be normal.
🫘 Nephrotic Syndrome
Massive urinary albumin loss leads to hypoalbuminemia and falsely low total calcium.
🍽️ Malnutrition
Protein-calorie malnutrition reduces albumin synthesis. Common in the elderly, hospitalized patients, and those with chronic disease.
🔥 Critical Illness
ICU patients have hypoalbuminemia from inflammation, capillary leak, and fluid resuscitation — corrected calcium clarifies true status.
📐 Formula
Corrected Calcium (Payne, 1973)
Corrected Ca = Measured Ca + 0.8 × (4.0 − Albumin)
* Each 1 g/dL drop in albumin shifts total calcium by ≈ 0.8 mg/dL
* Normal albumin reference = 4.0 g/dL
* If albumin is normal, correction ≈ 0 (unnecessary)
* Most accurate assessment: direct ionized calcium (iCa) measurement
Corrected Ca = Measured Ca + 0.8 × (4.0 − Albumin)
* Each 1 g/dL drop in albumin shifts total calcium by ≈ 0.8 mg/dL
* Normal albumin reference = 4.0 g/dL
* If albumin is normal, correction ≈ 0 (unnecessary)
* Most accurate assessment: direct ionized calcium (iCa) measurement
❓ Frequently Asked Questions
What is corrected calcium? ▼
About 40% of calcium is bound to albumin. When albumin drops, total calcium falls proportionally even when physiologically active (ionized) calcium is unchanged. Correction restores a meaningful estimate.
When to use corrected calcium? ▼
When albumin is outside its reference range, especially in cirrhosis, nephrotic syndrome, malnutrition, and critical illness. If albumin ≈ 4.0 g/dL, correction adds nothing.
Corrected vs ionized calcium? ▼
Ionized calcium is gold standard (ICU, dialysis, acid-base disturbances, massive transfusion). Corrected calcium is a pragmatic screen when iCa is unavailable or the patient is outpatient.
What causes hypercalcemia? ▼
Outpatient: primary hyperparathyroidism. Inpatient: malignancy (PTHrP, bony metastases, multiple myeloma). Also vitamin D toxicity, thyrotoxicosis, sarcoidosis, prolonged immobilization, thiazides, lithium.
🔗 Related Calculators
⚠️ Disclaimer — Educational reference only; not for direct clinical decision-making. In ICU or acid-base disturbance settings, ionized calcium is preferred.
References: Payne RB et al. Interpretation of serum calcium in patients with abnormal serum proteins. BMJ. 1973;4(5893):643-646.
References: Payne RB et al. Interpretation of serum calcium in patients with abnormal serum proteins. BMJ. 1973;4(5893):643-646.