Thyroid UK
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Help needed with Synacthen results

Just got my Synacthen test results back as follows:

0mins 296.4 nmol/L (Greater than 140)

30mins 533.4 nmol/L

60mins 589.6 nmol/L

From what I can gather there should be an increase >200nmol/L from baseline with a 30mins level >550nmol/L for 'normal' adrenal function. However some studies indicate the 60mins level as a better indicator, so I'm not sure which is correct?

Could this be a reason for persistent hypothyroid symptoms despite adequate T4 levels (18.6 pmol/L) on 200mcg Levothyroxine?

Also note latest FT3 level is 5.2 pmol/L (3.9 - 6.8) which continues the downward trend from previous results of 6.38 (Nov 17) and 5.73 (Feb 18).

7 Replies

As you have Hashimoto's you are likely to struggle to keep vitamin levels up. Have these been retested?


Hi SlowDragon,

Thanks for replying but not sure how that answers the specific questions raised?


Synacthen test looks like it shows good response

You asked about presistent symptoms

Well low vitamins can be cause of persistent symptoms despite appearing to be euthyroid

Looking at previous posts. Your ferritin has fallen a lot at every test.

Have you had B12 and folate tested.

See Box 1. Towards end of article

Some possible causes of persistent symptoms in euthyroid patients on L-T4

You will see low vitamin D, folate, ferritin and B12 listed

As FT3 is dropping you may simply not be on high enough dose of Levo.

Dr Toft, past president of the British Thyroid Association and leading endocrinologist, states in Pulse Magazine,

"The appropriate dose of levothyroxine is that which restores euthyroidism and serum TSH to the lower part of the reference range - 0.2-0.5mU/l.

In this case, free thyroxine is likely to be in the upper part of its reference range or even slightly elevated – 18-22pmol/l.

Most patients will feel well in that circumstance. But some need a higher dose of levothyroxine to suppress serum TSH and then the serum-free T4 concentration will be elevated at around 24-28pmol/l.

This 'exogenous subclinical hyperthyroidism' is not dangerous as long as serum T3 is unequivocally normal – that is, serum total around T3 1.7nmol/l (reference range 1.0-2.2nmol/l)."

You can obtain a copy of the articles from Thyroid UK email print it and highlight question 6 to show your doctor

 please email Dionne at

Professor Toft recent article saying, T3 may be necessary for many otherwise we need high FT4 and suppressed TSH in order to have high enough FT3

In past, before TSH tests, Levo doses were typically between 200-400mcg

Many, many Hashimoto's patients find gluten is a hidden problem and changing to strictly gluten free diet may help,


Vitamin levels are good so that is not the issue.

Ferritin levels are lower than I would like but I can’t supplement as:

Serum iron is high

Iron saturation level is high

HCT is high

HGB is high

Synacthen test does show a good response in terms of increase but from what I can gather the final level is still quite low?

Also from responses to last post I understood there would be no benefit in raising levo?


If FT3 continues to fall at next test, you have two options. Either a further increase in Levo or addition of small dose of T3

Many of us with Hashimoto's do need T3 because gut is compromised.

But you probably need to be strictly gluten free too, or certainly need to try it.

Ideally ask GP for coeliac blood test first

You do not need any gut symptoms to still have leaky gut and gluten issues


I’ll ask at my next endo appointment and hopefully he’ll play nice.

Is it generally the case that NDT seems to be more beneficial than T3 alone to those with Hashimoto’s? I’m sure I’ve also read that it also help sluggish adrenals to recover (but then again that might also be my imagination pulling a fast one whilst my brain is in the blender)?


No with Hashimoto's, T3 more likely beneficial. very very few UK Endo's will prescribe NDT

Certainly need to keep eye on antibodies if try it.

T4 plus T3 is more flexible in being able to vary doses of the two


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