ChemPath: Clinical Chemistry CPC

Question 1

Describe the effect of hypokalaemia on the myocardium.

Answer 1

Increases the myocardial irritability.

Question 2

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

Answer 2

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

Question 3

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

Answer 3

• 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 4

What is a Pott’s fracture?

Answer 4

Ankle fracture involving the tibia and fibula

Question 5

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

Answer 5

Microscopic haematuria

Question 6

What is the physiological role of PTHrP?

Answer 6

• 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 7

Name and describe an eye sign of hypercalcaemia.

Answer 7

• 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 8

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

Answer 8

Calcium stones are radio-opaque

Urate stones are radiolucent

Question 9

List some complications of hypercalcaemia.

Answer 9

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

Question 10

List some risk factors for hypercalcaemia.

Answer 10

Family history

Dehydration

Hyperparathyroidism

Question 11

Which bacterium has a predilection to infect urinary tract stones?

Answer 11

Proteus mirabilis

Question 12

What are the main investigations used for urinary tract stones?

Answer 12

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

Question 13

What are some management options for urinary tract stones?

Answer 13

• Lithotripsy
• Cystoscopy
• Lithotomy

Question 14

How can urinary tract stones be prevented?

Answer 14

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

NOTE: loop diuretics increase urine calcium

Question 15

At what point would you use emergency management of hypercalcaemia?

Answer 15

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

Question 16

Outline the emergency management of hypercalcaemia.

Answer 16

• 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 17

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

Answer 17

• 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

Question 18

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

Answer 18

Liver failure - they have a tendency to retain salt

Question 19

Outline the treatment of non-emergency hypercalcaemia.

Answer 19

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

Question 20

What is minimally invasive parathyroidectomy?

Answer 20

• 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 21

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

Answer 21

Cystic changes in the radial aspect

Question 22

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

Answer 22

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

Question 23

What is the mainstay of treatment of sarcoidosis?

Answer 23

Steroids

Question 24

What is the histological hallmark of sarcoidosis?

Answer 24

Non-caseating granulomas