Endocrine diagnostics

Question 1

How should you be using tests?

Answer 1

Tests don’t ‘give us the answer’

They are another piece of the ‘making a diagnosis’ jigsaw puzzle

The test result is added information for you to decide:

• I think this patient has ‘this’ endocrine condition
• I don’t think this patient has ‘this’ endocrine condition • Tests must be used and interpreted in the clinical context

Therefore assess the patient first
• History
• Physical Examination

Then ask - What tests would be helpful for me to:
• Confirm the diagnosis
• Refute (exclude) the diagnosis

Question 2

What is the pre-test probability?

Answer 2

the probability of a patient having the disorder before a diagnostic test results is known

in practical terms, gauged by history and examination findings

Question 3

What diagnostics tests should you use?§

Answer 3

Blood Tests vs Imaging in Endocrine Diagnostics In endocrinology, get the biochemistry sorted before doing the imaging

• Imaging can generate false positives
• e.g. adrenal or pituitary ‘incidental-omas’ or thyroid nodules on imaging of no clinical significance

If I do this test, how will it change the way that I manage this patient?

Can use the Imperial computer to search for tests.

Question 4

What is a static blood test?

Answer 4

snapshot in time of hormone levels in the patient’s when the blood test was taken at the clinic, we could do a ‘snap-shot’ test of blood levels of:

• cortisol, CTH, sodium, potassium
• glucocorticoid contributes to regulation of plasma sodium and potassium

Question 5

What is the importance of time of day for static blood tests?

Answer 5

• Many hormones are secreted according to a 24 hour circadian cycle
• If measured at the wrong time of day the hormone can appear to be low
• If we look at our example of measuring cortisol levels in the blood
• Cortisol levels in the blood are highest first thing in the morning
• If we had done the blood tests at 4pm after clinic
• Blood cortisol levels will be low – in everyone
• Therefore cannot be interpreted

Question 6

What is the importance of pulsatility for static blood tests?

Answer 6

Many hormones are secreted in pulses

• Transiently high levels of the hormone in the blood
• In a patient whose adrenals are producing little or no cortisol
• The pituitary secretes more ACTH to try to stimulate the failing adrenal glands
• Therefore a patient with adrenal failure should have high ACTH levels
• ACTH release is pulsatile
• Blood test might be taken during a pulse
• High ACTH on blood test results
• Blood test might be taken after a pulse
• Low ACTH on blood test result

(See diagram 15/20)

Question 7

What is a pulse? (When talking about pulsatility for static blood tests)

Answer 7

a burst of hormone release from the gland

Question 8

What are the dynamic blood tests?

Answer 8

Do I think the patient has too much hormone?
• Suppression test (if they do not respond then can confirm positive)

Do I think the patient has too little hormone?
• Stimulation test (if they do not respond then can confirm positive)

Question 9

What other things do you have to take into factor for dynamic blood tests?

Answer 9

• Logistics: staff, hospital visit, cost
• Patient acceptability: e.g. some tests can take a long time, multiple blood samples taken
• Safety e.g. insulin tolerance test

• Interpretation

• How low is ‘low’ in a suppression test?
• How high is ‘high’ in a stimulation test?

Question 10

How should you interpret the results?

Answer 10

• Look at your pre-test probability

• My pre-test probability suggested the patient does not have the condition
- Results support the clinical picture of the patient not having the condition

• My pre-test probability suggested the patient does have the condition
- Results support the clinical picture of the patient having the condition

• My pre-test probability and the results are not concordant

–> troubleshoot

Question 11

What should troubleshooting results compose of?

Answer 11

• Look at your patient:

• Conditions are not fixed but evolve over time
• Has something changed?

• Look at the pre-test probability:

• I do/don’t think the patient has the condition
• Interpret the result in this context

• Look at the logistics of the test:

• Wrong patient
• Time of day/pulsatility not taken into account
• Sample not handled properly (e.g. prolonged time to lab resulting in hormone degradation in the tube)
• Lab error (e.g. faulty assay)

• If things remain puzzling and difficult to explain:
- Repeat the test