Concerning not taking thyroxine before blood tests.

[Guest guest]

I have finally arranged an appointment with my GP to ask for the battery of

blood tests that is recommended by this forum and came to consider once again

the question of whether or not to take my thyroxine as normal before the tests.

The evidence quoted to not take it is as follows:

" The problem with using free T4 measurements if a patient is taking thyroxine is

that the level fluctuate after taking thyroxine treatment. Therefore, within the

few hours after ingestion there can be a ten or fifteen per cent level

difference in level compared to twelve to twenty four hours after ingestion. The

second problem which is frequently encountered by endocrinologists is that the

patients may not adhere to their treatment very strictly and may remember to

take a tablet before a blood test which will give them normal T4 levels and

might have omitted their tablets over the preceding weeks. Because of the

sensitivity of the pituitary that can be identified by raised TSH but a normal

free T4. Therefore, TSH, because it is measuring a response of the body, in this

case the pituitary gland, it is by far the best measure of the nature and degree

of thyroid hormone replacement. "

This very clearly says that taking thyroxine before a blood test will affect the

T4 levels. It does NOT say that it would affect TSH or T3 levels. Are we sure

that thyroxine should not be taken before these tests even when our doctors tell

us we should take the dose as normal?

Thanks,

Sharon