10. Calcium Metabolism and Disorders of Calcium Balance

Question 1

Why is calcium absorption in the GIT considered incomplete?

Answer 1

Requires activated vitamin D

Calcium containing salts aren’t absorbed

Question 2

What happens to the calcium that is ingested?

Answer 2

1/2 is absorbed
Some lost in stool
In a steady state, remaining calcium is excreted in urine

Question 3

What form is calcium stored as in bone?

Answer 3

Hydroxyapatite

Question 4

How is calcium reabsorbed in the kidneys?

Answer 4

Only ionised calcium is filtered
Some reabsorbed passively
Active under endocrine control

Question 5

What are the forms of calcium in circulation?

Answer 5

40% bound to albumin
15% bound to citrate, nitrate and phosphate
45% ionised/free

Question 6

How does hypoalbuminaemia affect calcium balance?

Answer 6

Less bound to albumin

Question 7

How does alkalosis affect calcium balance?

Answer 7

More bound calcium

Question 8

Which hormone reacts first to a dip in calcium?

Answer 8

PTH: peptide

Question 9

What effect does PTH have on the GIT?

Answer 9

Increases absorption of calcium and phosphate

Question 10

What is the overall effect of PTH?

Answer 10

Increase calcium but reduce phosphate

‘Phosphate Trashing Hormone’

Question 11

What effect does PTH have on bone?

Answer 11

Increases number and activity of osteoclasts

Increased bone resorption

Question 12

What effect does PTH have on the kidneys?

Answer 12

Increase calcium absorption in the distal nephron
Increase 1a hydroxylase enzyme activity > increased calcitriol
Increased excretion of phosphate into urine

Question 13

What effect does calcitriol have on the GIT?

Answer 13

Increased TRPV6 channels to increase calcium absorption

Question 14

What effect does calcitriol have on the bone?

Answer 14

Bind to osteoblasts and osteocytes

Increase pyrophosphate levels which inhibits calcium uptake into bone

Question 15

What effect does calcitriol have on the kidneys?

Answer 15

Increase TRPV5 channels and calbindin D28K
-increases resorption in distal tubule
No loss of phosphate

Question 16

What are the clinical effects of hypercalcaemia?

Answer 16

Stones
Bones
Groans
Psychiatric overtones
Short QT interval
Dehydration (diuretic effects)
Chronic kidney disease due to deposition
Nephrogenic diabetes insipidus (reduced response to ADH)
Type 1 renal tubular acidosis

Question 17

What are the causes of hypercalcaemia?

Answer 17

PTH excess
Vitamin D excess
Bone turnover
Thiazide diuretics

Question 18

What is the most common cause of hypercalcaemia in asymptomatic outpatients?

Answer 18

Hyperparathyroidism

Question 19

What is the most common cause of hypercalcaemia in in-patients?

Answer 19

Malignancy

Immobility

Question 20

Give causes of PTH excess

Answer 20

Hyperparathyroidism
Familial hypocalciuric hypercalcaemia
PTHrP secreting cancer
Lithium

Question 21

What diseases can cause vitamin D excess?

Answer 21

Granulomatous disorders can secrete ectopic calcitriol

eg. sarcoid, TB

Question 22

What are the reasons for hormone independent bone turnover?

Answer 22

Bone mets
Paget’s disease
Hyperthyroidism
Immobilisation

Question 23

How is a diagnosis of hypercalcaemia made?

Answer 23

Correct for hypoalbuminaemia
Physical exam and CXR
PTH level
-if suppressed check PTHrP, calcidiol, calcitriol

Question 24

How is serum calcium corrected for hypoalbuminaemia?

Answer 24

(0.02 x (40-albumin)) + serum calcium

Question 25

How does a physical exam and chest x ray help in the diagnosis of hypercalcaemia?

Answer 25

Cancer should be obvious at this stage | Granulomatous disease on CXR

Question 26

What does high PTH suggest?

Answer 26

Primary hyperparathyroidism

Question 27

What does high PTHrP suggest?

Answer 27

Malignancy

Question 28

What does high calcidiol suggest?

Answer 28

Vitamin D excess

Question 29

What does high calcitriol but not calcidiol suggest?

Answer 29

Ectopic calcitriol production

Question 30

What is the treatment for hypercalcaemia?

Answer 30

``` 0.9% saline Furosemide Bisphosphonates Calcitonin Steroids Parathyroidectomy ```

Question 31

Why is furosemide given?

Answer 31

Prevents resorption of calcium

Question 32

What bisphosphonate is given and why?

Answer 32

Pamidronate IV | Reduces bone resorption

Question 33

What side effect is associated with bisphosphonates?

Answer 33

Osteonecrosis of the jaw

Question 34

Why is calcitonin given?

Answer 34

Lowers osteoclast activity, but weak action

Question 35

Why are steroids given?

Answer 35

In granulomatous disease

Question 36

What are the symptoms of hypocalcaemia?

Answer 36

``` Tetany, spasms, cramps Perioral parasthesia Chvostek's sign (facial nerve) Hyperreflexia Trousseau's sign (pinching hand) ```

Question 37

What are the causes of hypocalcaemia?

Answer 37

``` Hypoparathyroidism Vitamin D deficiency Increased bone uptake Pancreatitis (saponification) Transfusions Alkalosis Chronic kidney disease ```

Question 38

What are the causes of hypoparathyroidism?

Answer 38

Autoimmune Surgery Low Mg

Question 39

What are the causes of vitamin D deficiency?

Answer 39

Lack of sunlight | Low CYP450

Question 40

How does chronic kidney disease cause tertiary hyperparathyroidism?

Answer 40

Low calcitriol due to reduced 1a hydroxy enzyme and increased phosphate as GFR too low to excrete Reduced GIT, renal and bone resorption of calcium Results in low ionised calcium and high phosphate -increased PTH > Increases calcium Causes chronic kidney disease mineral bone disorder Results in vascular calcifications and adenoma in parathyroid

Question 41

What else should be measured in hypocalcaemia?

Answer 41

``` PTH Creatinine Phosphate Magnesium Calcidiol and calcitriol ```

Question 42

What are the test results for primary hypoparathyroidism?

Answer 42

Low PTH | high phosphate

Question 43

What are the test results in chronic kidney disease?

Answer 43

High creatinine | Low calcitriol

Question 44

What is the treatment for hypocalcaemia?

Answer 44

Oral calcium Vitamin D Magnesium IV slow infusion

Question 45

What is the treatment for severe hypocalcaemia symptoms?

Answer 45

10ml of 10% calcium gluconate over 10 mins

Question 46

What is the preferred form of vitamin D to give in hypocalcaemia?

Answer 46

Calcidiol in general | In chronic kidney disease and hypoparathyroidism calcitriol preferred as they can't convert to calcidiol