Diagnostic biochemistry of calcium and bone disorders

Question 1

Which stimuli causes parathyroid hormone to be released?

Answer 1

fall in plasma ionised calcium (acute)

rise in plasma phosphate (chronic)

Question 2

What are the commonest causes of hypercalcaemia?

Answer 2

malignancy and primary hyperparathyroidism

Question 3

What does hypercalcaemia and suppressed PTH suggest?

Answer 3

non-parathyroid cause e.g. malignancy, vit D excess, sarcoidosis

Question 4

What does hypercalcaemia and raised (or detectable) PTH suggest?

Answer 4

PTH mediated cause e.g. primary and tertiary hyperparathyroidism (+ calcium receptor defects)

Question 5

What are the different hyperparathyroid states?

Answer 5

Primary parathyroid disorder: (adenoma, hyperplasia etc.). plasma calcium is high.
Secondary: normal response to chronic hypocalcaemia (e.g. CRF, malabsorption). plasma calcium is low/normal.
Tertiary: develops from prolonged secondary state. PTH secretion becomes autonomous. plasma calcium is high.

Question 6

What does hypocalcaemia and increased PTH suggest?

Answer 6

Non-parathyroid cause e.g. vit D deficiency, renal failure

Question 7

What does hypocalcaemia and low/normal PTH suggest?

Answer 7

Parathyroid cause e.g. hypoparathyroidism, Mg deficiency

Question 8

What are the markers of bone turnover for bone formation?

Answer 8

Osteoblasts:
alkaline phosphatase
bone alkaline phosphatase
collagen peptides