Corrected Calcium Calculator
Correct serum calcium for low albumin levels. About 40% of calcium binds to albumin, so hypoalbuminemia causes falsely low total calcium measurements.
Normal range: 8.5-10.5 mg/dL (2.1-2.6 mmol/L)
Normal range: 3.5-5.0 g/dL (35-50 g/L)
Correction Formula
Corrected Ca = Measured Ca + 0.8 × (4.0 - Albumin)
For every 1 g/dL decrease in albumin below 4, add 0.8 mg/dL to calcium.
Why Correct for Albumin?
About 40% of serum calcium is bound to albumin. When albumin is low (malnutrition, liver disease, nephrotic syndrome), total calcium appears falsely low even though the physiologically active ionized calcium may be normal. Correction estimates true calcium status.
Calcium Categories
Common Causes
Hypocalcemia
- Vitamin D deficiency
- Hypoparathyroidism
- Chronic kidney disease
- Hypomagnesemia
- Acute pancreatitis
Hypercalcemia
- Hyperparathyroidism
- Malignancy
- Vitamin D toxicity
- Thiazide diuretics
- Granulomatous disease
Frequently Asked Questions
Ionized calcium is preferred in: critically ill patients, significant acid-base disturbances (pH affects calcium binding), transfusion with citrated blood products, cardiopulmonary bypass, and when corrected calcium doesn't match clinical picture. It's the gold standard but less commonly available.
The 0.8 correction factor is an approximation. Studies show variable accuracy, especially in critically ill patients. The formula tends to overcorrect in some situations. When precision matters, ionized calcium measurement is superior. The correction remains clinically useful for screening.
High albumin (usually from dehydration/hemoconcentration) can falsely elevate total calcium. The formula would subtract from measured calcium. However, true hyperalbuminemia is rare. If albumin is elevated, consider dehydration as a cause and assess volume status.
Yes. Alkalosis increases calcium binding to albumin, lowering ionized calcium (can cause tetany even with normal total calcium). Acidosis decreases binding, raising ionized calcium. This is why ionized calcium is preferred in acid-base disorders. The correction formula doesn't account for pH.
Classic symptoms of hypercalcemia: Stones (kidney stones), Bones (bone pain, osteoporosis), Groans (abdominal pain, constipation, pancreatitis), Moans (psychiatric - depression, confusion, fatigue). Also: polyuria, polydipsia, shortened QT on ECG.
Clinical Pearls
- 90% rule: Primary hyperparathyroidism and malignancy cause 90% of hypercalcemia
- Check magnesium: Low Mg prevents PTH secretion and action
- ECG changes: Hypocalcemia → long QT; Hypercalcemia → short QT
- Symptoms threshold: Usually symptomatic when Ca >12 mg/dL or <7 mg/dL
Medical Disclaimer: This calculator provides estimates for educational purposes. Clinical decisions should consider symptoms, trends, and the complete clinical picture. Severe calcium abnormalities require urgent evaluation and treatment.