№ 17Endocrinology14 min read
Hypoparathyroidism, hypocalcaemia
1. Big picture
This topic is the opposite of hyperparathyroidism: too little biologically effective parathyroid hormone (PTH), or resistance to PTH, causing low calcium and usually high phosphate.
For the exam, always start hypocalcaemia with:
Is the PTH response appropriate?
Because normally, low calcium should strongly stimulate PTH.
| Calcium | PTH | Think |
|---|---|---|
| Low Ca + low/inappropriately normal PTH | true hypoparathyroidism | |
| Low Ca + high PTH | vitamin D deficiency, chronic kidney disease, malabsorption, PTH resistance | |
| Low Ca + low Mg | functional hypoparathyroidism due to magnesium deficiency |
The emergency pattern is:
perioral tingling + carpopedal spasm/tetany + seizures/laryngospasm/prolonged QT → acute symptomatic hypocalcaemia → IV calcium now.
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