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This is a clinician-written, evidence-based summary aligned to the USMLE Step 2 CK Content Outline. It is intended for medical students preparing for USMLE Step 2 CK. Management reflects current ACC/AHA, USPSTF, and APA guidelines. Always cross-reference with UpToDate, institutional protocols, and clinical judgment.
The Bottom Line
- Confirm hypocalcemia with corrected calcium or ionized calcium
- Symptoms reflect neuromuscular irritability: perioral numbness, paresthesias, cramps, tetany, seizures
- ECG clue: prolonged QT interval
- Most common hypoparathyroidism cause: post-thyroidectomy or neck surgery
- Severe symptomatic hypocalcemia: IV calcium gluconate; chronic hypoparathyroidism: oral calcium + calcitriol
Overview
Hypocalcemia occurs when ionized calcium is low enough to increase neuromuscular excitability and cardiac repolarization time. Major causes include hypoparathyroidism, vitamin D deficiency, chronic kidney disease, hypomagnesemia, pancreatitis, massive transfusion, sepsis, tumor lysis, rhabdomyolysis, and medications such as bisphosphonates or denosumab. Hypoparathyroidism causes low calcium and high phosphate because PTH is absent or inadequate.
Epidemiology
Postoperative hypoparathyroidism after thyroidectomy or parathyroid surgery is the most common acquired cause of hypoparathyroidism. Autoimmune hypoparathyroidism, DiGeorge syndrome, infiltrative disease, and activating calcium-sensing receptor mutations are less common. Vitamin D deficiency is common in the general population and may cause hypocalcemia when severe, particularly with malabsorption, limited sun exposure, chronic kidney disease, or anticonvulsant use.
Clinical Features
Symptoms
Perioral numbness, fingertip paresthesias, muscle cramps
Tetany, carpopedal spasm, laryngospasm
Seizures or altered mental status in severe hypocalcemia
Palpitations or syncope from prolonged QT/arrhythmia
Chronic symptoms: dry skin, brittle nails, cataracts, basal ganglia calcifications
Signs
Chvostek sign: facial twitch with tapping facial nerve
Trousseau sign: carpal spasm after BP cuff inflation — more specific than Chvostek
Hyperreflexia and muscle spasm
Prolonged QT interval on ECG
Neck surgery scar suggesting postoperative hypoparathyroidism
Investigations
First-line
Corrected total calcium or ionized calciumIonized calcium is preferred when albumin abnormality, critical illness, or acid-base disturbance is present
PTHLow/inappropriately normal PTH = hypoparathyroidism; high PTH = secondary response such as vitamin D deficiency or CKD
Magnesium and phosphateHypomagnesemia can impair PTH release/action; high phosphate supports hypoparathyroidism or CKD
ECGEvaluate QT prolongation or arrhythmia in symptomatic patients
Second-line
25-OH vitamin DAssesses vitamin D deficiency as cause or contributor
Renal functionCKD causes phosphate retention and reduced calcitriol production
Urinary calciumMonitor chronic hypoparathyroidism treatment and hypercalciuria risk
Specialist
Genetic or autoimmune evaluationIf early-onset, recurrent candidiasis, adrenal insufficiency, DiGeorge features, or family history
Brain imagingIf chronic hypoparathyroidism with movement disorder or seizures suggesting basal ganglia calcification
1
Severe or symptomatic hypocalcemia
- IV calcium gluconate with cardiac monitoring
- Correct magnesium deficiency because calcium will not normalize if magnesium remains low
- Treat seizures, laryngospasm, or arrhythmia as emergency complications
2
Mild/asymptomatic hypocalcemia
- Oral calcium carbonate or citrate
- Vitamin D replacement; use calcitriol when hypoparathyroidism or advanced CKD prevents activation
- Address cause: vitamin D deficiency, malabsorption, medication effect, CKD, hypomagnesemia
3
Chronic hypoparathyroidism
- Oral calcium + active vitamin D (calcitriol) to keep calcium in low-normal range
- Monitor serum calcium, phosphate, magnesium, creatinine, and urine calcium
- Avoid overtreatment because hypercalciuria can cause nephrolithiasis and nephrocalcinosis
4
Prevention after thyroid/parathyroid surgery
- Monitor calcium and PTH postoperatively
- Treat hungry bone syndrome with calcium and calcitriol when severe bone remineralization follows parathyroidectomy
Complications
- Seizures and laryngospasm: Severe neuromuscular irritability can be life-threatening
- Arrhythmia: Prolonged QT predisposes to torsades de pointes
- Cataracts and basal ganglia calcifications: Chronic hypoparathyroidism complications
- Nephrolithiasis/nephrocalcinosis: Can result from chronic calcium/calcitriol overtreatment
- Hungry bone syndrome: Profound hypocalcemia after parathyroidectomy for severe hyperparathyroidism
USMLE Step 2 CK Exam Tips
- 1Hypocalcemia prolongs QT; hypercalcemia shortens QT
- 2Post-thyroidectomy patient with perioral numbness and carpopedal spasm = hypoparathyroidism
- 3Low calcium + high phosphate + low PTH = hypoparathyroidism
- 4Low calcium + low magnesium: replace magnesium or hypocalcemia will persist
- 5Trousseau sign is more specific than Chvostek sign
- 6Severe symptomatic hypocalcemia = IV calcium gluconate
- 7Chronic hypoparathyroidism uses calcitriol because PTH is needed to activate vitamin D in kidneys
practicetest your knowledge on hypocalcemia & hypoparathyroidismApply what you've learnt with USMLE Step 2 CK-style questions from the iatroX Q-Bank — endocrine and beyond.
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