Endocrine diagnostics (19)

Question 1

A 23yr old patient feels very tired all the time, has lost weight (6kg over 4 months), and feels dizzy when he stands up. His family thinks he looks more tanned. What should we do next after GP referral?

Answer 1

See the patient in the endocrinology clinic, take a history and perform a physical examination

history:

• very tired
• weak
• poor appetite
• nauseated
• dizzy when stands up
• 6kg weight loss
• looks tanned without holiday

physical examination:

• mucosal and skin hyperpigmentation
• hypotension
• weight loss/anorexia
• -> strongly suggests that patient has primary adrenal failure (Addison’s)
• -> do blood tests in the morning (N.B. imaging can generate false positives e.g. thyroid nodule of no clinical significance)

Question 2

What is the pre-test probability?

Answer 2

• the probability of a patient having a specific disorder before a diagnostic test result is known
• in practice, gauged by history and examination findings

Question 3

What is a static blood test and what factors do we need to take into account?

Answer 3

• snap shot in time of hormone levels in the patient when blood test was taken
• many hormones are secreted according to a 24h circadian cycle e.g. ACTH peaks in morning, so cortisol levels are highest first thing in morning
• if measured at wrong time of day, hormone can appear to be low
• don’t take into account pulsatility of hormone secretion

Question 4

What are dynamic blood tests?

Answer 4

• suppression test if we suspect there is too much hormone
• stimulation test if we suspect there is too little hormone
• can cause patient harm e.g. insulin tolerance test leads to hypoglycaemia
• interpretation: how high or how low?

Question 5

How do we do a stimulation test for cortisol production?

Answer 5

• inject a supra-physiological dose of synthetic ACTH
• do the adrenals respond by producing cortisol? measured on blood tests
• if the adrenals do respond- do they respond well enough? is the rise in cortisol high enough?
• if the adrenals don’t respond to synthetic ACTH- no/low cortisol on blood tests–> give glucocorticoid replacement tablets

Question 6

What do we do if the pre-test probability and results are not concordant?

Answer 6

troubleshoot:

• look at patient- has something changed?
• look at pre-test probability and interpret results in context
• look at logistics of test- wrong patient? time of day? sample not handled properly? lab error?
• if things remain difficult to explain, repeat test