ChemPath: Clinical Chemistry CPC

Question 1

Describe the effect of hypokalaemia on the myocardium.

Answer 1

Increases the myocardial irritability - resulting in arrhythmias

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. Anterior displacement of the head of the radius (towards the back of hand
• 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

Complete the urine dip results for each condition:
- Renal stones
- Glomerulonephritis
- DKA
- Acute rheumatic fever
- Subacute bacterial endocarditis

Answer 6

• Renal stones –> painful macroscopic haematuria
• Glomerulonephritis –> painless microscopic haematuria
• DKA —> acidosis, ketonuria
• Acute rheumatic fever –> proteinuria
• Subacute bacterial endocarditis –> microemboli, microscopic haematuria

Question 7

If someone presents with renal stones what other investigation should you do?

Answer 7

You should find out why the patient got the stones in the first place - first line check blood calcium and PTH levels.

Question 8

What is the physiological role of PTHrP?

Answer 8

• PTHrp also acts on PTH receptor but has different actions.
• This is important in foetal life because it allows us for transplacental calcium transportation (calcium from mum to move to foetus for development)
• Can be released in cancers and result in similiar hyperparathyroidism and hypercalcaemia symptoms.

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

List some risk factors for hypercalcaemia.

Answer 10

Family history

Dehydration

Hyperparathyroidism

Question 11

List some complications of hypercalcaemia.

Answer 11

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

Question 12

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

Answer 12

Calcium stones are radio-opaque

Urate stones are radiolucent

Question 13

Risk factors for renal calcium stones

Answer 13

FHx
Hypercalcuria
Dehydration
Hypercalcaemia
Recurrent UTI

Question 14

Presentation of renal calcium stones

Answer 14

Painful haematuria
Renal failure
Recurrent infections

Question 15

Which bacterium has a predilection to infect urinary tract stones?

Answer 15

Proteus mirabilis

Question 16

What are the main investigations used for urinary tract stones?

Answer 16

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

Question 17

What are some management options for urinary tract stones?

Answer 17

• Expectant management with adequate analgesia (PR diclofenac)
• Lithotripsy (US waves to break stone - painful)
• Cystoscopy
• Lithotomy

Question 18

How can urinary tract stones be prevented?

Answer 18

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

NOTE: loop diuretics increase urine calcium

Question 19

At what point would you use emergency management of hypercalcaemia?

Answer 19

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

Question 20

Outline the emergency management of hypercalcaemia.

Answer 20

• 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 21

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

Answer 21

Liver failure - they have a tendency to retain salt

Question 22

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

Answer 22

• 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
• Helpful for bone mets but not given in all circumstances.

Question 23

Outline non-urgent hypercalcaemia treatment

Answer 23

1. Adequate hydration
2. Avoid thiazides
3. TUC (parathyroidectomy or treat malignancy)

Question 24

What is minimally invasive parathyroidectomy?

Answer 24

• A technetium 99m sestamibi 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 25

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

Answer 25

Subperiosteal resorption
Cystic changes in the radial aspect

Question 26

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

Answer 26

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

Histology of bone shows multinucleate giant cells

Question 27

Most helpful investigation in sarcoidosis

Answer 27

CXR - Bilateral hilar lymphadenopathy

Question 28

What is the histological hallmark of sarcoidosis?

Answer 28

Non-caseating granulomas

Question 29

Mechanism of hypercalcaemia in sarcoidosis

Answer 29

Macrophages in lungs express 1-alpha hydroxylase which activate vitamin D resulting in excessive calcium absorption.

PTH is suppressed to undetected levels.

Question 30

What is the mainstay of treatment of sarcoidosis?

Answer 30

IV Methylprednisolone (Steroids)

Question 31

MEN 1 and 2 can present with

Answer 31

hypercalcaemia