Diabetes Cases

Question 1

3. State the equation for osmolality.

Answer 1

Osmolality = 2(Na + K) + urea + glucose

Question 2

4. What is the anion gap?

Answer 2

There should always be a small gap between anions and cations due to the contribution of anions that are not measured
Normal ~ 18 mM

Question 3

5. List some causes of high anion gap.

Answer 3

Ketosis
Lactic acidosis
Methanol
Ethylene glycol poisoning

Question 4

6. How does an increase in plasma pH affect serum calcium levels?

Answer 4

As pH increases, plasma proteins start to stick to calcium more than usual
Total plasma calcium levels will remain normal but there will be less free ionised calcium (active form)
This leads to tetany (which can make patients hyperventilate even more)

Question 5

7. Why do patients with hyperosmolar hyperglycaemic state become unconscious?

Answer 5

It causes dehydration of the brain

Question 6

8. What is the danger of giving lots of fluids to someone with HHS?

Answer 6

It can cause cerebral oedema, so 0.9% saline should be used to achieve a slower reduction in plasma sodium

Question 7

9. What is a major consequence of metformin overdose?

Answer 7

Lactic acidosis

Question 8

10. Describe the Cori cycle. How does metformin affect this?

Answer 8

Lactate is produced by anaerobic glycolysis in the muscles
This goes to the liver and is converted back to glucose which will then return to the muscle
Metformin inhibits hepatic gluconeogenesis (the conversion of lactic acid to glucose in the liver) thereby resulting in lactic acidosis
NOTE: excess lactic acid is normally excreted by the kidneys, but in renal failure the kidneys cannot handle the excess lactic acid

Question 9

11. What is biochemical definition of diabetes mellitus?

Answer 9

Fasting blood glucose > 7.0 mmol/L

Question 10

12. How are the results of an oral glucose tolerance test (75 g glucose) interpreted?

Answer 10

Impaired glucose tolerance = 7.8 – 11.1 mM at 2 hours

Diabetes = > 11.1 mM at 2 hours

Question 11

13. What is the difference between pink puffers and blue bloaters in COPD?

Answer 11

Pink puffers – very breathless, because they are still sensitive to CO2 which rises due to poor lung function in COPD
Blue bloaters – the brain stops responding to rising CO2 so you are not breathless and the CO2 will continue to rise