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Endocrine
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Hypocalcemia Workup
Flowchart
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Always check magnesium before chasing PTH.
Decision
Outcome
Decision
Low Ca confirmed (corrected for albumin or ionized). First questions?
✓
Low magnesium, drugs (bisphosphonates, foscarnet), recent transfusion (citrate)?
✗
Order PTH immediately
Decision
Mg / drug / transfusion etiology?
✓
Yes → treat underlying + replete Mg; IV Ca if severe symptoms
✓
No → check PTH
Outcome
Replete magnesium; IV calcium gluconate for tetany/seizure/QT prolongation
Decision
PTH level?
✓
Low or normal → hypoparathyroidism
✓
High → vit D deficiency, CKD, pancreatitis, sepsis, tumor lysis, pseudohypoparathyroidism
Outcome
Hypoparathyroidism: post-surgical (most common), autoimmune (APS-1), genetic (DiGeorge, CaSR), infiltrative
Outcome
Replace vitamin D (if deficient); treat underlying disease
Pseudohypoparathyroidism: high PTH, low Ca, no response to PTH (end-organ resistance).