Are FSH always correct?

Hi,
I have had symptoms for 2 years, now 43, but I also have Hashimotos and Graves disease. took RAI 131 May 18. My periods were normal in the past, but for almost 2 years came early, like every 21 or 22 days, some were scant some heavy. Have the other symptoms too, night sweats, a little weight gain, muscle/joint aches/fatigue, thankfully the depression/anxiety has left ..they can also be thyroid I know, now it's been six weeks since a period, I feel like I have PMS, didn't think I was pregnant, but checked anyway, and it is negative. I had two FSH test  the last being April 07, and was told I was a long way from menopause. Could RAI have changed that fact? Also had normal OB check 5 months ago, I'm not miserable with this, and don't want to take anymore hormones, just my synthroid, but am curious if FSH is always correct, and can it change in a few months? My Grandmom stopped having periods at 38, my mom was in her 50's......I'm hoping that with the thyroid being so screwed up that I went through some menopausal symptoms w/o noticing alot.
Thanks for taking my question.

[Machelle Seibel, MD]

FSH is a hormone produced by the pituitary gland, a small gland just at the base of the brain. It is produced in pulses that occur about every few hours, so values are always fluctuating. As menopause approaches, these fluctuations are around a hight baseline and are wider in range. Estrogen makes FSH lower so when menopause comes and Estrogen is lower, FSH gets higher.  If your symptoms have started more recently than your last FSH test, it is possible that FSH has changed and the only way to tell is to repeat the test. Your thyroid level could also be changing, and if your estrogen is getting lower, that affects your thyroid hormone levels as well. Thyroid levels can take several months or even up to 6 months to equilibrate. RAI should not affect your FSH level.
Machelle M. Seibel, MD