Disorders of calcium balance

Question 1

What are the two sides of the constant dynamic calcium balance?

Answer 1

Osteoclasts breaking bone down to release calcium and osteoblasts building it up and using circulating calcium

Question 2

What are the two forms of blood calcium?

Answer 2

Ionised free form - physiologically important

Ultra-filterable - bound to protein

Question 3

What is the normal range for ionised free calcium?

Answer 3

2.10-2.60mmol/L

Question 4

How is ionised free calcium calculated?

Answer 4

Total calcium is measured then calcium correction can be used to work out the free calcium. Every g albumin <40g/L multiply by 0.02 and add to measured calcium, every g albumin >40g/L multiply by 0.02 and subtract from measured calcium

Question 5

What causes stimulation of the parathyroid glands?

Answer 5

Low serum calcium or high potassium

There is negative feedback from 1,25(OH)2 vitamin D and high calcium

Question 6

What are the three main effects of parathyroid hormone?

Answer 6

It causes increased reabsorption of calcium in the renal tubules
It causes increased vitamin D conversion in the kidneys which causes increased calcium uptake in the gut
It causes decreased phosphate reabsorption to lower phosphate levels

Question 7

What are the renal symptoms of hypercalcaemia?

Answer 7

Polyuria, polydipsia

Question 8

What are the GI symptoms of hypercalcaemia?

Answer 8

Vomiting, anorexia, constipation, abdo pain

Question 9

What are the neurosymptoms of hypercalcaemia?

Answer 9

Confusion, lethargy and depression

Question 10

What are the chronic effects of hypercalcaemia?

Answer 10

Bone pain, fractures and renal stones

Question 11

What are the main causes of hypercalcaemia?

Answer 11

Primary or tertiary hypercalcaemia
Hypercalcaemia of Malignancy (ectopic PTHrP and lytic bony mets)
Vitamin D intoxication

Question 12

By what mechanism can sarcoidosis cause hypercalcaemia?

Answer 12

There is production of active vitamin D within the granulomas

Question 13

How is vitamin D intoxication treated?

Answer 13

With steroids as they decrease GI absorption of vitamin D

Question 14

What tests should be done for suspected hyperparathyroidism?

Answer 14

Bloods show increased calcium and increased parathyroid hormone in primary
Increased parathyroid hormone and low or normal calcium
Also decreased phosphate
In tertiary there is increased PTH and normal or high calcium as the PTH levels have been high for so long from chronic disease
Imaging may show decreased bone density e.g. osteoporosis on DEXA

Question 15

What are the causes of primary hyperparathyroidism?

Answer 15

80% are solitary adenomas

20% are hyperplasia of all glands

Question 16

What are the causes of secondary hyperparathyroidism?

Answer 16

Decreased vitamin D intake, renal failure cause the parathyroid to compensate and start to produce more parathyroid hormone

Question 17

What are the causes of tertiary hyperparathyroidism?

Answer 17

This is when a cause of secondary hyperparathyroidism is corrected e.g. correcting renal failure
The glands have undergone hyperplastic change and continue to secrete excess parathyroid hormone despite negative feedback

Question 18

What is the treatment for primary hyperparathyroidism?

Answer 18

Increase fluid intake to avoid stones and increase calcium and vit D intake in mild disease
Excision of the adenoma may be required

Question 19

What is the treatment of acute hypercalcaemia?

Answer 19

Lots of fluids to dilute calcicum

Biphosphonates e.g. alendronic acid to lower calcium and encourage bone take up of calcium

Question 20

How is hypoparathyroidism treated?

Answer 20

With calcium supplements and synthetic PTH