Hypercalcemia and Hypocalcemia¶
Chapter 57 | Part 2: Cardiovascular and Metabolic Disorders
KEY CLINICAL POINTS¶
- Primary hyperparathyroidism and malignancy are the leading causes of hypercalcemia, while hypoparathyroidism and vitamin D deficiency are major causes of hypocalcemia.
- Calcium homeostasis is regulated by PTH, vitamin D metabolites, and renal excretion, with serum calcium maintained within 8.5–10.5 mg/dL.
- Severe hypercalcemia requires immediate intravenous hydration and bisphosphonates, while hypocalcemia is managed with calcium supplementation and vitamin D correction.
1. DEFINITION & OVERVIEW¶
Hypercalcemia and hypocalcemia represent abnormal serum calcium levels, with critical implications for organ function. Hypercalcemia is defined as serum calcium >10.5 mg/dL (2.6 mmol/L), while hypocalcemia is <8.5 mg/dL (2.1 mmol/L). Calcium is essential for bone structure, neuromuscular function, and hormone secretion, with homeostasis regulated by parathyroid hormone (PTH), vitamin D, and renal excretion.
Table 57-1: Causes of Hypercalcemia¶
| Category | Causes |
|---|---|
| Excessive PTH Production | Primary hyperparathyroidism, tertiary hyperparathyroidism, FHH, parathyroid carcinoma |
| Malignancy-Related | PTHrP overproduction, lytic bone metastases, granulomatous diseases (sarcoidosis, TB), vitamin D intoxication |
| Other Causes | Hyperthyroidism, immobilization, milk-alkali syndrome, thiazides, denosumab discontinuation, rhabdomyolysis recovery |
Table 57-2: Causes of Hypocalcemia¶
| Category | Causes |
|---|---|
| Low PTH Levels | Hypoparathyroidism (surgical, autoimmune, genetic), FHH, vitamin D deficiency |
| High PTH Levels | Secondary hyperparathyroidism (renal failure, vitamin D deficiency, malabsorption), pseudohypoparathyroidism |
| Other Causes | Hypomagnesemia, drug-induced (calcium channel blockers, bisphosphonates), alkalosis, rhabdomyolysis, hypoproteinemia |
1.1 Calcium Homeostasis¶
Serum calcium is tightly regulated by PTH, 1,25(OH)2D, and renal excretion. PTH increases bone resorption and renal calcium reabsorption, while 1,25(OH)2D enhances intestinal absorption. Hypocalcemia triggers PTH release, whereas hypercalcemia suppresses it.
1.2 Clinical Relevance¶
Hypercalcemia can cause nephrocalcinosis, cardiac arrhythmias, and bone pain, while hypocalcemia leads to tetany, seizures, and neuromuscular irritability. Both conditions require prompt diagnosis and targeted management.
2. EPIDEMIOLOGY¶
Hypercalcemia is common in older adults and patients with malignancy, while hypocalcemia is more prevalent in postmenopausal women and those with renal disease. Primary hyperparathyroidism affects ~0.01% of the population, whereas hypoparathyroidism is rare but often iatrogenic (e.g., thyroid surgery). Vitamin D deficiency is widespread, especially in elderly populations and those with limited sun exposure.
2.1 Risk Factors¶
Hypercalcemia risk factors include malignancy, chronic kidney disease, and thiazide use. Hypocalcemia is associated with vitamin D deficiency, renal failure, and malnutrition. Genetic disorders like FHH and DiGeorge syndrome increase susceptibility.
3. ETIOLOGY & PATHOPHYSIOLOGY¶
Hypercalcemia arises from excessive PTH, vitamin D, or bone resorption. Hypocalcemia results from PTH deficiency, impaired vitamin D activation, or reduced intestinal absorption. Pathophysiology involves disrupted CaSR signaling, altered PTH feedback, and renal excretion abnormalities.
3.1 Hypercalcemia Mechanisms¶
Primary hyperparathyroidism (pHPT) causes excessive PTH, leading to bone resorption and renal calcium reabsorption. Malignancy-associated hypercalcemia is due to PTHrP or vitamin D overproduction. Granulomatous diseases activate CYP27B1, converting 25(OH)D to 1,25(OH)2D.
3.2 Hypocalcemia Mechanisms¶
Hypoparathyroidism impairs PTH secretion, while vitamin D deficiency reduces intestinal absorption. Hypomagnesemia disrupts CaSR function, and alkalosis increases calcium binding to albumin. Malabsorption syndromes (e.g., celiac disease) reduce calcium uptake.
4. CLINICAL FEATURES¶
Hypercalcemia presents with fatigue, constipation, and renal stones, while severe cases cause confusion, arrhythmias, and renal failure. Hypocalcemia manifests as paresthesias, tetany, and seizures. Chronic hypercalcemia may lead to osteoporosis, whereas hypocalcemia causes muscle weakness and cardiac arrhythmias.
4.1 Hypercalcemia Symptoms¶
Mild: fatigue, constipation, polyuria. Severe: confusion, arrhythmias, renal failure, bone pain. Complications include nephrocalcinosis and pathologic fractures.
4.2 Hypocalcemia Symptoms¶
Mild: paresthesias, Chvostek/Trousseau signs. Severe: tetany, seizures, prolonged QTc, cardiac arrhythmias. Chronic cases may present with muscle weakness and osteomalacia.
5. DIFFERENTIAL DIAGNOSIS¶
Hypercalcemia: pHPT, malignancy, granulomatous disease, vitamin D intoxication. Hypocalcemia: hypoparathyroidism, vitamin D deficiency, hypomagnesemia, alkalosis. Use the mnemonic 'VITAMINS TRAP' to guide differentiation.
5.1 Hypercalcemia Differentials¶
Primary hyperparathyroidism, malignancy (PTHrP), sarcoidosis, thiazide use, milk-alkali syndrome, immobilization.
5.2 Hypocalcemia Differentials¶
Hypoparathyroidism, vitamin D deficiency, hypomagnesemia, malnutrition, renal failure, drug-induced (bisphosphonates, calcium channel blockers).
6. INVESTIGATIONS & DIAGNOSIS¶
Measure total and ionized calcium, correct for albumin, and assess PTH, phosphate, and vitamin D levels. Urinary calcium excretion and 25(OH)D/1,25(OH)2D ratios help differentiate etiologies. Use the 'VITAMINS TRAP' mnemonic for differential diagnosis.
6.1 Diagnostic Tests¶
Serum calcium (corrected for albumin), PTH, phosphate, magnesium, 25(OH)D, 1,25(OH)2D, creatinine, and urinary calcium. Consider parathyroid imaging and bone density scans.
6.2 Algorithms¶
- Correct calcium for albumin. 2. Measure PTH. 3. Assess vitamin D and phosphate. 4. Evaluate for malignancy, renal disease, or drug use. 5. Use imaging for parathyroid adenomas or metastases.
7. MANAGEMENT & TREATMENT¶
Mild hypercalcemia requires hydration and monitoring, while severe cases need bisphosphonates, calcitonin, or denosumab. Hypocalcemia is managed with calcium gluconate, vitamin D, and magnesium supplementation. Address underlying causes (e.g., malignancy, renal failure).
7.1 Hypercalcemia Treatment¶
- IV fluids (4–6 L saline in 24 h). 2. Bisphosphonates (zoledronic acid, pamidronate). 3. Calcitonin (4–8 IU/kg q6h). 4. Denosumab for renal failure. 5. Glucocorticoids for sarcoidosis or lymphoma.
7.2 Hypocalcemia Treatment¶
- IV calcium gluconate (1–2 g in 500 mL D5W). 2. Vitamin D analogs (calcitriol, doxercalciv). 3. Magnesium supplementation. 4. Address underlying causes (e.g., parathyroidectomy for hypoparathyroidism).
8. PROGNOSIS & COMPLICATIONS¶
Hypercalcemia may lead to renal failure, osteoporosis, and cardiac arrhythmias. Hypocalcemia causes tetany, seizures, and cardiac instability. Early treatment improves outcomes, but chronic cases may result in irreversible bone disease or neurological damage.
8.1 Complications¶
Hypercalcemia: nephrocalcinosis, renal failure, arrhythmias. Hypocalcemia: tetany, seizures, prolonged QTc, cardiac arrest.
9. SPECIAL CONSIDERATIONS¶
Pregnancy: Monitor for hypercalcemia (malignancy) or hypocalcemia (vitamin D deficiency). Pediatrics: Hypoparathyroidism is often iatrogenic (surgery). Elderly: Higher risk of hypocalcemia due to renal insufficiency and malnutrition. Avoid calcium supplements in renal failure.
10. KEY POINTS & CLINICAL PEARLS¶
- Correct calcium for albumin using 0.8 mg/dL per 1 g/dL albumin decrement. 2. PTH suppression in hypercalcemia indicates malignancy or granulomatous disease. 3. Use bisphosphonates for severe hypercalcemia, and calcitonin for rapid correction. 4. Hypocalcemia requires calcium and vitamin D supplementation, with magnesium correction if present. 5. 'VITAMINS TRAP' mnemonic aids differential diagnosis.