Hypoparathyroid hypocalcemia vs PTH-resistant or vitamin D-deficient hypocalcemia
How to tell Hypoparathyroid hypocalcemia and PTH-resistant or vitamin D-deficient hypocalcemia apart when a board question makes them look alike.
Hypoparathyroid is PTH-low; pseudohypoparathyroid is PTH-high with high phosphate; vitamin D deficiency is PTH-high with low phosphate.
Side by side
Low calcium with high phosphate and low PTH after thyroid surgery, autoimmune disease, or DiGeorge syndrome, causing tetany, Chvostek sign, or Trousseau sign.
Pseudohypoparathyroidism type 1a has low calcium, high phosphate, high PTH, and Albright hereditary osteodystrophy; vitamin D deficiency has low calcium, low phosphate, high PTH, and poor mineralization.
Absent or low PTH reduces renal calcium reabsorption, vitamin D activation, and phosphate excretion.
PTH resistance blocks PTH signaling despite high hormone levels; vitamin D deficiency reduces intestinal calcium/phosphate absorption and triggers secondary PTH rise.
Low calcium, high phosphate, and low PTH support true hypoparathyroidism.
High PTH with high phosphate supports pseudohypoparathyroidism; high PTH with low phosphate and low vitamin D supports vitamin D deficiency.
The trap
All can cause tetany from low calcium, so PTH and phosphate direction decide the diagnosis.
The repair move
For hypocalcemia, read PTH first, then phosphate: low PTH, resistant PTH, or vitamin D deficiency.
Try a free question
CoreA patient develops perioral numbness and carpopedal spasm after thyroidectomy. Labs show low calcium, high phosphate, and low PTH. Which diagnosis is most likely?
Show answer and explanation
Answer: A. Hypoparathyroidism. Low calcium with high phosphate and low PTH after thyroid surgery points to hypoparathyroidism.
Why the other choices are tempting
- B. Pseudohypoparathyroidism has high PTH from end-organ resistance.
- C. Vitamin D deficiency usually has high PTH and low phosphate.
- D. Primary hyperparathyroidism causes high calcium with high PTH.
- E. Familial hypocalciuric hypercalcemia causes high calcium with low urinary calcium.
Flashcards
Tap a card to flip it.
What labs point to hypoparathyroidism?
Low calcium, high phosphate, and low PTH point to hypoparathyroidism.
What labs point to pseudohypoparathyroidism?
Low calcium, high phosphate, and high PTH point to PTH resistance.
Quick answers
What is the fastest way to tell Hypoparathyroid hypocalcemia from PTH-resistant or vitamin D-deficient hypocalcemia?
Hypoparathyroid is PTH-low; pseudohypoparathyroid is PTH-high with high phosphate; vitamin D deficiency is PTH-high with low phosphate.
What is the key clue for Hypoparathyroid hypocalcemia?
Low calcium with high phosphate and low PTH after thyroid surgery, autoimmune disease, or DiGeorge syndrome, causing tetany, Chvostek sign, or Trousseau sign.
What is the key clue for PTH-resistant or vitamin D-deficient hypocalcemia?
Pseudohypoparathyroidism type 1a has low calcium, high phosphate, high PTH, and Albright hereditary osteodystrophy; vitamin D deficiency has low calcium, low phosphate, high PTH, and poor mineralization.
What is the common trap with Hypoparathyroid hypocalcemia vs PTH-resistant or vitamin D-deficient hypocalcemia?
All can cause tetany from low calcium, so PTH and phosphate direction decide the diagnosis.