Hypercalcaemia

Question 1

Underlying causes of hypercalcaemia

Answer 1

Bone metastasis
Multiple myeloma
Hyperparathyroidism (primary and tertiary)
Vit D overdose

Question 2

Bone metastasis

Answer 2

ALP - high
PTH - low
Phosphate - high

Increased bone turnover results in increased ALP which causes hypercalcaemia and increased phosphate
(ALP is released by osteoblasts!!)

Question 3

Multiple Myeloma

Answer 3

ALP - normal
PTH - low
Phosphate - high

ALP is normal as osteoclasts are activated in MM while osteoblasts (which release ALP) are inhibited
Hypercalcaemia results from increased osteoclast activicty

Question 4

Hyperparathyroidism (primary and tertiary)

Answer 4

ALP - normal/high
PTH - normal/high
Phosphate - low

PTH causes increased bone turnover therefore you get increased ALP (normal if bone turnover is slow)
Bone turnover releases calcium and phosphate which results in hypercalcaemia
PTH increases renal excretion of phosphate which results in a low phosphate
A normal PTH is abnormal in this scenario as increased calcium should result in low PTH due to negative feedback of calcium on parathyroids (PTH should be low in presence of hypercalcaemia)

Question 5

Vit D overdose

Answer 5

ALP - low
PTH - low
Phosphate - high

Vit D causes increased absorption of calcium and phosphate from the gut resulting in hypercalcaemia and hyperphosphataemia.
Increased calcium suppresses PTH release from parathyroids
Low PTH results in low bone turnover which results in low ALP levels