Truest TSH results

My doctor suggests that I schedule a TSH test to measure my thyroid activity, since I have a long family history of thyroid disorders and I am showing symptoms of hypothyroidism. What is the best time of day and the best conditions for me to take this test so that the results are truest? (ie: should I fast or not, should I have been sedentary or have had physical exercise, etc.)Thanks for your time!

-Lori

[Kevin Pho, MD]

Hello - thanks for asking your question.

Thyroid function is best assessed by measuring serum TSH, assuming steady state conditions and the absence of pituitary or hypothalamic disease.

Measurement of serum TSH (rather than free T4 or total T4) is an excellent screening test for hypothyroidism in ambulatory patients being evaluated for nonspecific symptoms such as fatigue, depression, or menstrual irregularity. There are, however, three settings in which measurement of serum TSH may not be a useful tool for the diagnosis of hypothyroidism:

- If pituitary or hypothalamic disease is known or suspected.
- In hospitalized patients, since there are many other factors in acutely or chronically ill euthyroid patients that influence TSH secretion.
- In patients receiving drugs or with underlying diseases which affect TSH secretion. Drugs that can decrease TSH secretion include dopamine, glucocorticoids, phenytoin, and somatostatin analogues (such as octreotide). Drugs that increase TSH secretion include dopamine antagonists (metoclopramide or domperidone), amiodarone, and oral cholecystographic dyes (sodium ipodate).

Since TSH is a measure of steady-state thyroid function, factors such as time of day, fasting, or exercise should not affect the result.  

I stress that this answer is not intended as and does not substitute for medical advice - please see your personal physician for further evaluation of your individual case.

Thanks,
Kevin, M.D.

Links:
http://labtestsonline.org/understanding/analytes/tsh/glance.html

[mdamiani]

I've been diagnosed with hypothyroidism.  You can go to the lab at any hour of the day.  You should do this as soon as possible because if you are the doctor is going to put you on hormone so you start feelling better.  Don't worry about this.  You'll be fine.

[starion]

Call the lab & ask them about any recommendations regarding time of taking the test & any preparations.  The personnel are generally VERY helpful.  Good luck!
Starion