Why You Can't Trust Total Calcium
Routine blood tests measure Total Calcium. However, only about 50% of this calcium is biologically active ("Ionized Calcium"). The other half circulates attached to proteins, primarily Albumin.
If your Albumin levels are low (hypoalbuminemia)—common in malnutrition, liver disease, or post-surgery—your "Bound" calcium will drop, making your Total Calcium look frighteningly low. However, your active "Ionized" calcium might be completely normal. This is known as False Hypocalcemia.
When to Use This Correction
This calculation (Payne's Formula) is the standard bedside method for estimating true calcium status when Ionized Calcium testing is unavailable.
- ✓Use for patients with Albumin < 4.0 g/dL.
- ✓Use to rule out True Hypocalcemia before treating with calcium supplements.
- ✕Do NOT rely on this for patients with Stage 4/5 Kidney Disease (use Ionized Calcium instead).
Frequently Asked Questions
What are the symptoms of real Hypocalcemia?
True calcium deficiency (Corrected Ca < 8.5) often presents with neuromuscular irritability. Look for the "Chvostek sign" (facial twitching when tapped), "Trousseau sign" (hand cramping with blood pressure cuff), numbness in fingers/toes, and muscle cramps. Severe cases can lead to seizures or heart arrhythmias.
Does high protein intake raise albumin?
Not immediately. While Albumin is a protein made by the liver, serum levels are a slow indicator of nutritional status (half-life of 20 days). Low albumin is more often caused by inflammation (sickness) or liver disease than simple dietary protein lack. Eating a steak won't fix your calcium reading overnight.
What causes Hypercalcemia (High Calcium)?
A corrected calcium above 10.2 mg/dL is often a sign of Hyperparathyroidism (overactive parathyroid glands) or malignancy (cancer). It causes "Groans, Moans, Bones, and Stones" (Stomach pain, Fatigue, Bone pain, Kidney stones). It requires immediate medical investigation.
Is this formula accurate for kidney failure patients?
It is less accurate in Stage 4/5 CKD (Chronic Kidney Disease). In patients with renal failure, the binding properties of albumin change. Nephrologists generally prefer measuring Ionized Calcium directly for dialysis patients rather than relying on the Payne formula correction.
What is the normal range for Albumin?
A healthy serum albumin level is typically 3.4 to 5.4 g/dL. Levels below 3.4 suggest malnutrition, liver dysfunction, or acute inflammation. For every 1 g/dL drop in albumin below 4.0, total calcium usually drops by 0.8 mg/dL, necessitating this correction.
References
- National Institutes of Health (NIH). StatPearls: Corrected Calcium and Hypoalbuminemia.
- MDCalc. Calcium Correction Clinical Guidelines.
- British Medical Journal (BMJ). Assessment of Hypercalcemia.
- Mayo Clinic Laboratories. Calcium, Total and Ionized, Serum.
Tools & Data Verified by the EverydayCalculators Medical Research Team.
Last updated: January 2026.