Calcium is one of the most vital minerals in the human body, found primarily in bones, teeth, and cells. Beyond skeletal strength, calcium plays a central role in cardiovascular health, neuromuscular activity, endocrine function, blood clotting, and cellular signaling. For these processes to work efficiently, the body must maintain a serum calcium level between 9–11 mg/dL.
When this balance is disturbed, two conditions arise:
- Hypercalcemia: Calcium levels rise above 11 mg/dL.
- Hypocalcemia: Calcium levels fall below 9 mg/dL.
Both conditions can disrupt body functions, sometimes becoming life-threatening if untreated. Calcium imbalance is not just a biochemical problem; it affects nearly every organ system. Understanding it is essential for doctors, nurses, medical students, and patients alike.
The Physiology of Calcium
To appreciate calcium imbalance, one must first understand its normal role:
- Bone and Teeth Formation: Around 99% of the body’s calcium is stored in bones and teeth as hydroxyapatite, giving them rigidity and strength.
- Cardiovascular Function: Calcium regulates cardiac muscle contraction, electrical conduction, and blood pressure.
- Neuromuscular Transmission: Calcium is essential for nerve impulse transmission and muscle contraction.
- Endocrine Regulation: Acts as a second messenger in hormone secretion and intracellular signaling.
- Blood Clotting (Coagulation): Calcium (factor IV) is critical in the coagulation cascade.
The delicate balance of calcium is maintained by:
- Parathyroid hormone (PTH): Increases calcium by stimulating bone resorption and kidney reabsorption.
- Vitamin D (Calcitriol): Enhances intestinal absorption of calcium.
- Calcitonin: Lowers calcium by inhibiting bone resorption.
This triad ensures serum calcium remains within its tight physiological window.
Hypercalcemia: Too Much Calcium in the Blood
Definition
Hypercalcemia is diagnosed when serum calcium exceeds 11 mg/dL. Even mild elevations can cause symptoms, while severe hypercalcemia (>14 mg/dL) may become a medical emergency.
Mnemonic for Symptoms: “BACKME”
- B – Bone pain
- A – Arrhythmias
- C – Cardiac arrest (bounding pulses)
- K – Kidney stones
- M – Muscle weakness (↓ deep tendon reflexes)
- E – Excessive urination (polyuria)
These symptoms reflect calcium’s effect on bone metabolism, renal function, cardiovascular conduction, and neuromuscular excitability.
Causes & Risk Factors of Hypercalcemia
1. Increased Calcium Absorption
- High vitamin D intake
- Granulomatous diseases (e.g., sarcoidosis, tuberculosis – where activated macrophages increase vitamin D activity)
2. Decreased Calcium Excretion
- Kidney disease (impaired renal clearance)
- Thiazide diuretics (promote calcium reabsorption in the distal tubule)
3. Increased Bone Resorption
- Hyperparathyroidism (primary, secondary, tertiary)
- Malignancy (bone metastases, multiple myeloma, PTHrP-secreting tumors)
4. Other Causes
- Hemoconcentration (dehydration)
- Prolonged immobilization (bone calcium release)
- Lithium therapy
Clinical Features of Hypercalcemia
- Musculoskeletal: Bone pain, muscle weakness, pathological fractures.
- Renal: Kidney stones, nephrocalcinosis, polyuria, dehydration.
- Cardiac: Arrhythmias, shortened QT interval, bradycardia, cardiac arrest.
- Neurological: Confusion, lethargy, stupor, coma.
- Gastrointestinal: Constipation, nausea, vomiting, abdominal pain.
Diagnosis of Hypercalcemia
- Serum calcium levels: >11 mg/dL (corrected for albumin).
- PTH levels: Differentiate primary hyperparathyroidism (high PTH) from malignancy (low PTH, high PTHrP).
- ECG changes: Shortened QT interval, widened T waves.
- Imaging: Bone scans or skeletal X-rays in malignancy-related hypercalcemia.
Management of Hypercalcemia
1. Stop calcium and vitamin D intake (IV or PO supplements).
2. Discontinue thiazide diuretics.
3. Hydration with IV saline: Dilutes calcium and promotes renal excretion.
4. Loop diuretics (Furosemide): Enhance calcium excretion (avoid thiazides).
5. Pharmacological agents:
- Calcitonin (rapid onset, short-lived effect).
- Bisphosphonates (e.g., pamidronate, zoledronic acid) for malignancy-induced hypercalcemia.
- NSAIDs (prostaglandin inhibitors, reduce bone resorption).
- Corticosteroids (reduce vitamin D–mediated absorption in granulomatous disease).
6. Dialysis: In refractory cases or renal failure.
7. Dietary advice: Avoid calcium-rich foods.Hypocalcemia: Too Little Calcium in the Blood
Definition
Hypocalcemia occurs when serum calcium falls below 9 mg/dL. Severe cases (<7 mg/dL) are dangerous and may cause seizures, tetany, and arrhythmias.
Mnemonic for Symptoms: “CATS”
- C – Convulsions
- A – Arrhythmias (diminished pulses)
- T – Tetany
- S – Spasms & stridor
Also: GO NUMB – Numbness in fingers, face, and limbs.
Classic Clinical Signs
- Trousseau’s Sign: Carpal spasm when inflating a BP cuff (due to neuromuscular irritability).
- Chvostek’s Sign: Facial muscle twitching when tapping over the facial nerve. Remember: “C” for Cheesy Smile.
Causes & Risk Factors of Hypocalcemia
1. Inhibition of Calcium Absorption
- GI malabsorption syndromes (celiac disease, Crohn’s disease).
- Vitamin D deficiency.
- Post-gastrectomy or bariatric surgery.
2. Increased Calcium Excretion
- Kidney disease, diuretic phase.
- Chronic diarrhea, steatorrhea.
- Wound drainage.
- Hypoalbuminemia (low binding protein).
- Pancreatitis (fatty acids bind calcium).
- Sepsis, alkalosis.
Clinical Features of Hypocalcemia
- Neuromuscular: Tetany, seizures, paresthesias, cramps, laryngospasm.
- Cardiovascular: Prolonged QT interval, heart failure, hypotension.
- Skeletal: Bone deformities in chronic hypocalcemia (rickets, osteomalacia).
- Psychiatric: Anxiety, irritability, depression.
Diagnosis of Hypocalcemia
- Serum calcium <9 mg/dL (corrected for albumin).
- PTH levels: Low in hypoparathyroidism, high in secondary causes.
- ECG: Prolonged QT interval.
- Vitamin D levels.
Management of Hypocalcemia
1. Calcium supplementation:
- Oral calcium (calcium carbonate, calcium citrate).
- IV calcium gluconate (warm, dilute, and administer slowly to avoid arrhythmia).
2. Vitamin D supplementation:
- Ergocalciferol (D2) or Cholecalciferol (D3).
- Calcitriol for renal failure patients.
3. Adjunct therapies:
- Magnesium correction if low.
- Aluminum hydroxide (binds phosphate).
- Anticonvulsant precautions (seizure control).
Calcium-Phosphate Relationship
Calcium and phosphate exist in an inverse relationship.
- When calcium increases, phosphate decreases (e.g., hyperparathyroidism).
- When calcium decreases, phosphate increases (e.g., renal failure).
This relationship is crucial for interpreting lab reports and managing patients.
Complications of Calcium Imbalance
- Fracture risk: Both hyper- and hypocalcemia predispose to fractures due to bone fragility.
- Arrhythmias: Potentially fatal if not corrected.
- Seizures: Hypocalcemia-induced tetany may cause respiratory compromise.
- Renal impairment: Kidney stones and nephrocalcinosis in hypercalcemia.
- Chronic consequences: Osteoporosis, osteomalacia, growth impairment in children.
Quick Clinical Comparison Table
| Feature | Hypercalcemia (>11 mg/dL) | Hypocalcemia (<9 mg/dL) |
|---|---|---|
| Mnemonic | BACKME | CATS / GO NUMB |
| Cardiac | Short QT, arrhythmias, arrest | Prolonged QT, arrhythmias |
| Neurological | Confusion, weakness, coma | Tetany, convulsions, seizures |
| Renal | Stones, polyuria | Increased excretion, hypocalcemic crisis |
| Musculoskeletal | Bone pain, fractures | Spasms, cramps, rickets |
| Signs | — | Trousseau’s, Chvostek’s |
| Treatment | Stop Ca, fluids, bisphosphonates, calcitonin | Calcium + Vit D, seizure precautions |
Frequently Asked Questions (FAQ)
Q1. What is the normal calcium level in blood?
The normal serum calcium level is 9–11 mg/dL.
Q2. What are the earliest symptoms of calcium imbalance?
- Hypercalcemia: Excessive thirst, frequent urination, fatigue.
- Hypocalcemia: Tingling around the mouth, muscle cramps, numbness.
Q3. Which foods should be avoided in hypercalcemia?
Patients should limit calcium-rich foods like dairy products, fortified cereals, and supplements.
Q4. Can stress or lifestyle cause calcium imbalance?
Yes. Chronic stress, poor diet, alcohol abuse, and lack of sun exposure (vitamin D deficiency) contribute indirectly.
Q5. How are pathological fractures linked to calcium imbalance?
Imbalance weakens bones, increasing the risk of fragility fractures, especially in elderly and bedridden patients.
