34&35: Endocrinology Problem

Question 1

What are the DDx for thirst and frequency?

Answer 1

Drinking too much water - habit, psychological

Excess loss of water - renal, endocrine

Question 2

What are the DDx for fatigue and weight loss?

Answer 2

• Psychosocial (depression)
• Metabolic - diabetes mellitus
• Chronic infection - HIV, TB, postviral
• Chronic gut or heart or renal disease
• Cancer

Question 3

What are the ranges for fasting and post-prandial glucose?

Answer 3

Fasting
<5.6 mmol/L normal
5.6-6.9 impaired
> 7 = diabetes

Post prandial
<7.8 normal
7.8-11 impaired
>11 = diabetes

Question 4

Which haemoglobin test is an investigation for diabetes?

Answer 4

HbA1c

Question 5

What causes osmotic diuresis in DKA?

Answer 5

• Plasma glucose over tubular maxima, excess glucose lost in urine
• Reduced efficiency of loop of Henle (inc. flow)
• Unabsorbed glucose and ketone salts retaining water in DCT/CD
• Volume loss from ketone salts

Question 6

Effective osmolality = (2x measured ___) + measured ____

Answer 6

Effective osmolality = (2x measured Na) + measured glucose

Question 7

Glucose corrected serum sodium = measured ___ + . [___ - 5.5] x 0.288

Answer 7

Glucose corrected serum sodium = measured Na + . [glucose- 5.5] x 0.288

Question 8

Why do many patients with acute DKA develop renal failure?

Answer 8

• Acute volume loss -> activation of SNS and AII
• Causes afferent renal arteriolar constriction at expense of GFR
• Can cause acute renal failure

Question 9

What are the mechanisms that favour K loss in DKA?

Answer 9

• Inc plasma osmolality causes shift of fluid from ICF to ECF, inc gradient for K to exit cells
• Excretion in urine (aldosterone, polyuria)

Question 10

What is the effect of insulin on Na/K/ATPase?

Answer 10

• Stimulates

- Causes extrusion of Na and uptake of K into cells

Question 11

Why might mental state be altered after administering fluid to a patient with DKA?

Answer 11

• Cerebral oedema
• Over a few days has developed hyperosmotic state
• Sudden drop in ECF osmolality

Question 12

How do you differentiate between central and nephrogenic diabetes insipidus?

Answer 12

Central corrects with administration of desmopressin