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Adjust total calcium for albumin level to assess true calcium status
Normal: 8.5-10.5 mg/dL
Normal: 3.5-5.5 g/dL
Corrected Calcium = Total Calcium + 0.8 × (4 - Albumin)
This formula adjusts for the fact that ~40% of serum calcium is bound to albumin
| Corrected Calcium (mg/dL) | Category | Severity | Urgency |
|---|---|---|---|
| <7.0 | Severe Hypocalcemia | Grade 3-4 | Urgent |
| 7.0-8.0 | Moderate Hypocalcemia | Grade 2 | Prompt |
| 8.0-8.5 | Mild Hypocalcemia | Grade 1 | Monitor |
| 8.5-10.5 | Normal | None | Routine |
| 10.5-12.0 | Mild Hypercalcemia | Grade 1 | Investigate |
| 12.0-14.0 | Moderate Hypercalcemia | Grade 2-3 | Prompt treatment |
| >14.0 | Severe Hypercalcemia | Grade 4 | Emergency |
Approximately 40% of serum calcium is bound to albumin, 10% is bound to other anions, and 50% exists as free ionized calcium (the physiologically active form). When albumin levels are abnormal - common in critical illness, malnutrition, liver disease, and nephrotic syndrome - total calcium measurements can be misleading. The corrected calcium formula estimates the true calcium status by adjusting for albumin levels.
Hypercalcemia is one of the most common metabolic complications of cancer, occurring in 20-30% of patients during their illness:
Hypercalcemia affects multiple organ systems:
Treatment intensity depends on severity and symptoms:
Hypocalcemia has numerous causes requiring different management:
Direct measurement of ionized calcium is preferred in certain situations:
For patients with calcium abnormalities:
Ionized calcium is the gold standard as it measures the physiologically active form directly. However, it's not always available, requires special handling, and is affected by pH. Corrected calcium is a good estimate for most clinical situations. Use ionized calcium in critical illness, acid-base disorders, or when the corrected value doesn't match the clinical picture.
The correction formula becomes less accurate with severe hypoalbuminemia (<2.0 g/dL). In these cases, consider measuring ionized calcium directly. The formula may underestimate true calcium abnormalities in critically ill patients with severe hypoalbuminemia.
Severity guides urgency: Mild (10.5-12 mg/dL) and asymptomatic can be addressed non-urgently with outpatient workup. Moderate (12-14 mg/dL) or any symptomatic hypercalcemia warrants prompt treatment (same-day). Severe (>14 mg/dL) or causing altered mental status is a medical emergency requiring immediate hospitalization.
Three main mechanisms: 1) PTHrP (parathyroid hormone-related peptide) secretion by tumors mimics PTH action (most common, seen in lung, breast, kidney cancers). 2) Direct bone destruction from metastases releasing calcium (myeloma, breast cancer). 3) Increased vitamin D production by lymphomas. Treatment requires both acute calcium lowering and tumor-directed therapy.
Yes, multiple medications affect calcium. Hypercalcemia: excessive calcium/vitamin D supplements, thiazide diuretics, lithium. Hypocalcemia: bisphosphonates, denosumab, cinacalcet, proton pump inhibitors (impair absorption), chemotherapy, foscarnet. Always review medications when investigating calcium disorders.
Vitamin D (as active form calcitriol) is essential for intestinal calcium absorption and bone health. Check 25-OH vitamin D levels in hypocalcemia workup. Repletion is often needed. In cancer, some tumors produce excess calcitriol causing hypercalcemia. CKD patients need active vitamin D (calcitriol) as kidneys can't activate it.
Magnesium is essential for PTH secretion and action. Hypomagnesemia (<1.5 mg/dL) causes functional hypoparathyroidism and hypocalcemia that won't respond to calcium supplementation alone. Always check and correct magnesium first when treating hypocalcemia. Give magnesium sulfate 1-2g IV over 15 minutes if severe.
Hypercalcemia shortens the QT interval on ECG (opposite of hypocalcemia's prolonged QT). It can cause bradycardia, AV blocks, and increased sensitivity to digoxin. Severe hypercalcemia increases risk of arrhythmias and cardiac arrest. ECG monitoring is important in moderate-severe cases. Patients on digoxin are at particular risk.