ChemPath: Clinical Chemistry CPC

Question 1

Which biochemical changes may present with depression?

Answer 1

hypercalcaemia

Question 2

How may severe hypocalcaemia present?

Answer 2

paralysis

person may have a panic attack= hyperventilation which makes them alkalotic

calcium binds to proteins more strongly in alkalosis, leading to further hypocalcaemia

Question 3

Describe the effect of hypokalaemia on the myocardium.

Answer 3

Increases the myocardial irritability.

Question 4

Describe the cardiac consequences of plasma potassium being too high or too low.

Answer 4

• Too low - ventricular fibrillation
• Too high - asystole (ultimate stable rhythm)

Question 5

What is the difference between a Colles’ fracture and a Smith’s fracture?

Answer 5

• Colles’ - fracture caused by falling on an outstretched hand. The radial head will be displaced backwards (away from the palm).
• Smith’s - fracture caused by falling on a flexed wrist. The radial head will be displaced forwards (towards the palm)

Question 6

What is a Pott’s fracture?

Answer 6

Ankle fracture involving the tibia and fibula

Question 7

What would you expect to see on the urine dipstick of someone with subacute bacterial endocarditis?

Answer 7

Microscopic haematuria

Question 8

What is the physiological role of PTHrP?

Answer 8

• Our genome encodes a gene for PTHrP
• This is important in foetal life because it allows us to steal calcium from our mother to help form our skeleton

NOTE: PTHrP is also produced by the lactacting breast

NOTE: PTHrP stimulates cancer cells to invade bone

Question 9

Name and describe an eye sign of hypercalcaemia.

Answer 9

• Band keratopathy - calcium deposition across the front of the eye
• It is a feature of chronic hypercalcaemia (i.e. it will not be caused by hypercalcaemia of malignancy)

Question 10

What is a key difference between calcium stones and urate stones?

Answer 10

Calcium stones are radio-opaque

Urate stones are radiolucent

Question 11

3 differentials for hypercalcaemia

Answer 11

1. cancer- most common in hospital
2. primary hyperparathyroidism- most common in community
3. sarcoidosis

Question 12

List some complications of hypercalcaemia.

Answer 12

• Renal stones
• Pancreatitis
• Peptic ulcer disease
• Skeletal changes (osteitis fibrosa cystica)

Question 13

List some risk factors for renal calcium stones.

Answer 13

Family history

Dehydration

hypercalciuric >6mmol/L: stone formers

hypercalcaemia

Hyperparathyroidism

Question 14

presentation of renal stones

Answer 14

pain- colic

haematuria

infection

renal failure

Question 15

renal stones management

Answer 15

analgesia and supportive

lithotripsy

cystoscopy

lithotomy

thiazides can be used to reduce calcium

Question 16

Which bacterium has a predilection to infect urinary tract stones?

Answer 16

Proteus mirabilis

Question 17

What are the main investigations used for urinary tract stones?

Answer 17

• CT-KUB
• Stone analysis
• Urine and serum biochemistry

Question 18

What are some management options for urinary tract stones?

Answer 18

• Lithotripsy
• Cystoscopy
• Lithotomy

Question 19

How can urinary tract stones be prevented?

Answer 19

• Drink more water
• Treat hypercalciuria (thiazides)
• Treat hypercalcaemia

NOTE: loop diuretics increase urine calcium

Question 20

At what point would you use emergency management of hypercalcaemia?

Answer 20

When serum calcium > 3 mmol/L or very unwell (e.g. dehydrated, confused, drowsy, seizures)

Question 21

Outline the emergency management of hypercalcaemia.

Answer 21

• IV access
• Insert catheter
• 3-6 L 0.9% saline over 24 hours
• The first litre should be given quickly (over 1 hour) to correct dehydration
• Elderly patients should also be given furosemide (to prevent pulmonary oedema)

Question 22

Which other drug may be used under desperate circumstances when managing hypercalcaemia?

Answer 22

• 30-60mg Pamidronate (IV)
• Good at treating bone pain but takes at least 1 week to start working and gets incorporated into bone for a very long time so post-op, patient gets very bad hypocalcaemia

Question 23

In which group of patients would you used dextrose rather than saline?

Answer 23

Liver failure - they have a tendency to retain salt

Question 24

Outline the treatment of non-emergency hypercalcaemia.

Answer 24

• Keep well hydrated
• Avoid thiazides (they reduce hypercalciuria but they increase plasma calcium concentration)
• Surgery

Question 25

What is minimally invasive parathyroidectomy?

Answer 25

• A technetium sesta MIBI scan shows a hyperactive parathyroid
• An USS is also performed and if the results of the sesta MIBI and USS are concordant, the whole neck does not need to be opened
• If they are not concordant, the surgeon will need to view all four glands and take out the largest one

Question 26

What feature may you see on an X-ray of the hands in a patient with primary hyperparathyroidism?

Answer 26

Cystic changes in the radial aspect- outer bones more affected

Question 27

What is a characteristic histological feature of long-standing undiagnosed hyperparathyroidism?

Answer 27

Brown tumours - they are multinucleated giant cells in the bone. The giant cells are activated osteoclasts.

Question 28

Why will someone with sarcoidosis have hypercalcaemia?

Answer 28

macrophages in the lungs express 1a-hydroxylase, leading to more activated vit D production and more Ca2+ retention/ from bone

• seasonal hypercalcaemia in these patients

Question 29

What is the mainstay of treatment of sarcoidosis?

Answer 29

Steroids

Question 30

When would you want to give bisphosphonates early?

Answer 30

hyperCa of malignancy as stops PTHrp breaking down bone for calcium

Question 31

What is the histological hallmark of sarcoidosis?

Answer 31

Non-caseating granulomas