Hypocalcemia
Hypocalcemia is a reduction in serum ionized calcium, the biologically active form of calcium.calcium should not be checked daily as an “ICU routine.”Total calcium is useful for screening but is an unreliable indicator of ionized calcium, as ionized calcium is affected by factors such as pH, albumin, sodium, and phosphate concentrations.
Calcium exists in three forms:
Form | Percentage | Physiological role |
Ionized (free) | 45-50% | Active form |
Protein-bound (mostly albumin) | 40-45% | Inactive |
Complexed (citrate, phosphate, bicarbonate) | 10-15% | Inactive |
Normal values
Test | Normal |
Total calcium | 8.5–10.5 mg/dL (2.1–2.6 mmol/L) |
Ionized calcium | 1.12–1.32 mmol/L (4.5–5.3 mg/dL) |
Corrected Calcium
Low albumin decreases total calcium while ionized calcium remains normal.therefore no use of this formula.
Corrected calcium (mg/dL)= Measured Ca + 0.8 × (4 − albumin)
Limitations
- Unreliable in ICU, sepsis, CKD, liver disease, burns, and critical illness.
- Ionized calcium should always be measured when possible in critically ill patients.
Severity of Hypocalcemia
| Serum Calcium Level |
Mild | Total calcium: 8.0–8.5 mg/dL (2.0–2.12 mmol/L) Ionized calcium: 1.0–1.12 mmol/L |
Moderate | Total calcium: 7.0–8.0 mg/dL (1.75–2.0 mmol/L) Ionized calcium: 0.9–1.0 mmol/L |
Severe | Total calcium: <7.0 mg/dL (<1.75 mmol/L) Ionized calcium: <0.9 mmol/L |
Calcium Physiology
Organ | PTH | Calcitriol | Calcitonin |
Bone | ↑ Bone resorption → ↑ Ca²⁺ release | Promotes mineralization; with PTH can facilitate resorption when needed | ↓ Osteoclast activity |
Kidney | ↑ Ca²⁺ reabsorption, ↓ phosphate reabsorption, ↑ calcitriol synthesis(1,25 vitamin D -activated) | Mild ↑ Ca²⁺ reabsorption | Mild ↑ Ca²⁺ excretion |
Gastrointestinal Tract | Indirect effect via calcitriol | ↑ Calcium and phosphate absorption | No significant effect |
Functions of Calcium
Physiological Role of Calcium | Functions / Clinical Importance |
Neuromuscular Function | Stabilizes neuronal membranes, regulates nerve impulse conduction, and is essential for skeletal and smooth muscle contraction. Hypocalcemia lowers the threshold potential, causing increased neuromuscular excitability → tetany, muscle cramps, carpopedal spasm, laryngospasm, seizures. |
Cardiac Function | Essential for excitation–contraction coupling, myocardial contractility, SA node automaticity, and AV nodal conduction. Hypocalcemia may cause reduced cardiac output, hypotension, heart failure, prolonged QT interval, and ventricular arrhythmias (especially torsades de pointes). |
Coagulation | Calcium acts as Factor IV and is required for activation of multiple coagulation factors (II, VII, IX, X) and the anticoagulant proteins Protein C and Protein S. |
Cellular Signaling | Functions as a ubiquitous second messenger, mediating hormone secretion, neurotransmitter release, enzyme activation, gene transcription, and intracellular signal transduction. |
Bone & Teeth | Major structural component of hydroxyapatite; essential for bone mineralization, skeletal strength, remodeling, and tooth mineralization. |
Etiology
Cause of Hypocalcemia | Mechanism / Common Causes / Characteristic Features |
Reduced PTH (Hypoparathyroidism) | Mechanism: Decreased PTH secretion. Causes: Thyroid/parathyroid surgery (most common), autoimmune disease, congenital (DiGeorge syndrome), radiation, infiltrative disorders (hemochromatosis, Wilson disease). Labs: ↓PTH, ↓Calcium, ↑Phosphate. |
PTH Resistance (Pseudohypoparathyroidism) | End-organ resistance to PTH. Labs: ↑PTH, ↓Calcium, ↑Phosphate. May be associated with Albright hereditary osteodystrophy. |
Vitamin D Deficiency / Impaired Activation | Mechanism: Reduced intestinal calcium absorption. Causes: Poor intake, malabsorption, celiac disease, liver disease, CKD, limited sunlight exposure, anticonvulsants, bariatric surgery. |
Magnesium Disorders (Hypomagnesemia) | Most important reversible cause. Causes impaired PTH secretion and PTH resistance. Calcium will not normalize until magnesium is corrected. Causes: Alcoholism, diarrhea, PPIs, aminoglycosides, cisplatin, loop diuretics, tacrolimus, cyclosporine. |
Hyperphosphatemia | Excess phosphate binds calcium, causing calcium-phosphate precipitation and lowering ionized calcium. Causes: CKD, tumor lysis syndrome, rhabdomyolysis, phosphate enemas, massive phosphate administration. |
Acute Pancreatitis | Fat necrosis and saponification consume calcium; inflammation and hypoalbuminemia may contribute. Hypocalcemia is a marker of severe pancreatitis. |
Massive Blood Transfusion | Citrate in stored blood chelates ionized calcium. Risk is increased with massive transfusion, liver failure, hypothermia, shock, and ECMO. |
Chronic Kidney Disease (CKD) | Decreased calcitriol synthesis → reduced intestinal calcium absorption; hyperphosphatemia; secondary hyperparathyroidism. |
Drugs | Bisphosphonates, denosumab, cinacalcet, calcitonin, loop diuretics, phenytoin, phenobarbital, rifampicin, foscarnet, cisplatin, ketoconazole, PPIs (via hypomagnesemia). EDTA contamination of blood samples can cause pseudohypocalcemia. |
Critical Illness | sepsis, burns, trauma, ARDS, acute pancreatitis, CRRT, ECMO, massive transfusion, cytokine surge, catecholamine excess, PTH resistance and magnesium deficiency.Alkalosis |
Hungry Bone Syndrome | Occurs after parathyroidectomy (occasionally thyroidectomy). Rapid skeletal uptake of calcium, phosphate, and magnesium causes profound hypocalcemia. |
Osteoblastic Metastases | Increased calcium uptake into bone; classically seen with prostate cancer. |
Neonatal Causes | Prematurity, infants of diabetic mothers, maternal hyperparathyroidism, and birth asphyxia. |
Poisoning | Ethylene glycol poisoning.,Hydrofluoric acid |
Pseudohypocalcemia
- Low total calcium but Normal ionized calcium.
- Causes—Hypoalbuminemia,Critical illness,Nephrotic syndrome,Liver disease.
- No treatment needed.
Clinical Features
Symptoms depend on
- Ionized calcium
- Rapidity of fall
System | Clinical Manifestations of Hypocalcemia |
Neuromuscular | Perioral numbness, circumoral paresthesias, distal paresthesias, muscle cramps, tetany, carpopedal spasm, laryngospasm, bronchospasm, hyperreflexia, generalized seizures. |
Cardiovascular | Hypotension, reduced myocardial contractility, heart failure, shock, arrhythmias, prolonged QT interval, rarely torsades de pointes. |
Central Nervous System (CNS) | Confusion, irritability, anxiety, depression, psychosis, delirium, cognitive impairment, seizures. |
Chronic Manifestations | Dry skin, brittle nails, coarse hair/hair loss, cataracts, basal ganglia calcification, dental abnormalities (enamel defects, delayed eruption), extrapyramidal symptoms/Parkinsonism. |
Physical Signs
Clinical Sign | Method & Interpretation |
Chvostek Sign | Method: Tap the facial nerve just anterior to the ear (over the parotid region). Positive: Ipsilateral twitching of the facial muscles (corner of mouth, nose, or eye). Clinical significance: Suggests increased neuromuscular excitability due to hypocalcemia. Sensitivity is modest and the sign may be present in 10–25% of healthy individuals, making it less specific. |
Trousseau Sign(late sign) | Method: Inflate a blood pressure cuff to 20 mmHg above systolic pressure and maintain inflation for 3 minutes. Positive: Carpopedal spasm (wrist flexion, MCP flexion, IP extension, thumb adduction—”obstetrician’s hand”). Clinical significance: More sensitive and specific than Chvostek sign for latent hypocalcemia and indicates increased neuromuscular excitability. |
ECG Findings
- Prolonged QT interval
- prolonged ST segment(ST segment duration is inversely related to the ionized calcium level)
Less common
- AV block
- Ventricular arrhythmias
- Torsades de pointes (rare)
Investigations
Essential
- Ionized calcium (preferred in ICU)
- Total calcium
- Albumin
- Magnesium
- Phosphate
- Creatinine
- Urea
- Electrolytes
- ECG
Determine Cause
- PTH(normally be elevated in response to hypocalcemia.)
- 25-OH vitamin D
- 1,25 vitamin D (e.g., renal failure, hypoparathyroidism)
- LFT
- Amylase/lipase
- TSH (if autoimmune disease suspected)
- Urinary calcium (selected cases)
Diagnostic Approach
Laboratory finding | Likely diagnosis |
↓ PTH + ↑ phosphate | Hypoparathyroidism(↓ PTH in this only) |
↑ PTH + ↓ vitamin D | Vitamin D deficiency |
↑ PTH + ↑ phosphate + CKD | CKD |
↓ Mg | Magnesium deficiency |
↑ phosphate + tumor lysis | Phosphate-induced hypocalcemia |
Normal ionized Ca + low albumin | Pseudohypocalcemia |
Treatment
Step 1: Confirm true hypocalcemia
- Measure ionized calcium whenever possible.
- Correct magnesium first if low.
- Treat the underlying cause.
Most critically ill patients have mild-moderate hypocalcemia. Treatment usually isn’t indicated.
Indications for IV Calcium
- Symptomatic hypocalcemia
- ECG changes
- Ionized calcium <0.9 mmol/L
Contraindications / Cautions for IV Calcium Administration
- ⚠️ Hyperphosphatemia: because it can increase the calcium–phosphate product, promoting calcium phosphate precipitation in soft tissues and blood vessels (metastatic calcification/calciphylaxis)However, if severe symptomatic hypocalcemia is present (e.g., tetany, seizures, or life-threatening arrhythmias), IV calcium should not be withheld despite hyperphosphatemia.
- ⚠️ Ethylene glycol poisoning: it may enhance calcium oxalate crystal formation, potentially worsening tissue deposition (especially in the kidneys and, less commonly, other organs). The priority is prompt treatment with fomepizole (or ethanol if unavailable) and supportive care, with dialysis when indicated. IV calcium should be reserved for patients with clinically significant hypocalcemia or ECG changes.
- ⚠️ Digoxin use
IV Calcium Preparations
Calcium Gluconate
Preferred for peripheral IV administration.
- 10% calcium gluconate (10 mL ampoule) contains ≈93 mg elemental calcium (4.65 mEq; 2.3 mmol).
- Initial dose: 10–20 mL of 10% solution IV over 10–20 minutes with ECG monitoring.(Rapid administration may cause hypotension, bradycardia, and arrhythmias)
- May repeat if symptoms persist.
- For persistent hypocalcemia, follow with a continuous infusion titrated to ionized calcium.
Calcium Chloride
- 10% calcium chloride (10 mL) contains ≈272 mg elemental calcium (13.6 mEq; 6.8 mmol)—about three times more elemental calcium than calcium gluconate.
- Preferred during cardiac arrest or profound shock because of greater calcium delivery.
- Use through a central venous catheter whenever possible due to the risk of severe tissue necrosis with extravasation.
Continuous Infusion (if needed)
Patients with ongoing losses (e.g., pancreatitis, CRRT, massive transfusion, hungry bone syndrome) may require continuous IV calcium with frequent ionized calcium monitoring (every 4–6 hours initially) and dose adjustment.
Other uses Of IV calcium
- Hyperkalemia
- Hypermagnesemia
- Bradycardia(calcium-responsive bradycardias:Hyperkalemia,Hypocalcemia,Hypermagnesemia,Calcium-channel blocker toxicity ,Beta-blocker toxicity).
- Refractory shock with hypocalcemia
Oral Calcium
Used for mild or chronic hypocalcemia after stabilization.
Typical elemental calcium requirement: 1–3 g/day in divided doses. Increase to 6-12 grams/day elemental calcium in hungry Bone syndrome
Preparation | Approximate elemental calcium |
Calcium carbonate 1250 mg | 500 mg |
Calcium citrate 2380 mg | 500 mg |
Calcium carbonate requires gastric acid and is best taken with meals. Calcium citrate is preferred in patients taking PPIs or with achlorhydria.
Vitamin D deficiency
- Cholecalciferol (Vitamin D3) or ergocalciferol (Vitamin D2) replacement according to deficiency severity.
he dose depends on the severity of vitamin D deficiency, the clinical setting, and whether the patient has normal renal function. In patients with vitamin D deficiency causing hypocalcemia, cholecalciferol (Vitamin D3) is generally preferred over ergocalciferol (Vitamin D2) because it produces a greater and more sustained increase in serum 25-hydroxyvitamin D.
Vitamin D Status (25-OH Vitamin D)
25(OH) Vitamin D Level | Interpretation |
≥30 ng/mL (≥75 nmol/L) | Sufficient |
20–29 ng/mL (50–74 nmol/L) | Insufficiency |
<20 ng/mL (<50 nmol/L) | Deficiency |
<10–12 ng/mL (<25–30 nmol/L) | Severe deficiency |
Adults with Normal Renal Function
Vitamin D Insufficiency (20–29 ng/mL)
- Cholecalciferol (Vitamin D3):
- 800–2,000 IU orally daily, OR
- 60,000 IU orally once monthly
Maintenance after correction:800–2,000 IU/day
Vitamin D Deficiency (<20 ng/mL)
Preferred regimen (Endocrine Society):
- Cholecalciferol 50,000 IU orally once weekly for 6–8 weeks OR 6,000 IU orally daily for 8 weeks
- Then maintenance:1,500–2,000 IU/day
Severe Deficiency (<10 ng/mL) or Symptomatic Hypocalcemia
- Cholecalciferol 50,000 IU weekly for 8–12 weeks
- Continue 1,500–2,000 IU/day maintenance afterward.
If symptomatic hypocalcemia is present:
- Give IV calcium initially (if indicated).
- Start oral calcium (1–3 g elemental calcium/day).
- Add calcitriol 0.25–0.5 μg twice daily for rapid correction until vitamin D stores are replenished, because cholecalciferol requires several days to weeks to become effective.
Advanced CKD/hypoparathyroidism/Hungry bone syndrome
- Active vitamin D (calcitriol) is usually required because conversion to the active form is impaired.
Management depends on CKD stage.
CKD G1–G3
Treat vitamin D deficiency as in the general population using cholecalciferol or ergocalciferol.
CKD G4–G5 or Hypoparathyroidism
Nutritional vitamin D alone is often inadequate because renal conversion to active vitamin D is impaired.
Use:
- Calcitriol: 0.25–0.5 μg/day (may increase gradually every 4-8 weeks to 1–2 μg/day if needed)
- Alternatives:
- Alfacalcidol
- Paricalcitol (mainly for secondary hyperparathyroidism)
Monitoring
- Repeat ionized calcium 30–60 minutes after IV bolus, then every 4–6 hours until stable.
- Continuous ECG monitoring during IV calcium therapy.
- Monitor magnesium, phosphate, potassium, and renal function daily (or more frequently in unstable patients).
- Watch for extravasation, especially with calcium chloride.
Major Guideline and Reference Sources
- Harrison’s Principles of Internal Medicine (21st ed.)
- Irwin & Rippe’s Intensive Care Medicine
- Oh’s Intensive Care Manual