time of day for TSH test

[meadow20]

Does it really not matter what time of day you have blood drawn for the TSH test? Does it also not matter if you have eaten or not?
Does anyone know why or why not?

[stella5349]

I agree too.  Doctors say anytime - but in my last six years - getting on a routine of AM draws - empty stomach - before meds and definately help me maintain my levels.

[kitty9309]

I agree. TSH in early am. Take meds after blood draw as the free t4 can be affected by as much as +20% for several hours after ingestion of t4 meds.

I get mine drawn in the early am fasting so I can take my Levoxyl right after the blood draw on am empty stomach.

The following is from thyroidmanager.org:

Measured levels of free and total T4 are influenced by the interval between tablet ingestion and blood sampling. In athyreotic subjects who took 0.15-0.2 mg T4 orally, the serum free and total T4 concentrations were increased by about 20% one to four hours later, with return to baseline about nine hours after T4 ingestion; serum TSH and T3 levels showed no time-dependent variation (171).

[chel 81]

Thyroid levels and TSH fluctuate throughout the day so it is important to make a pattern of testing about the same time from test to test. This way if your TSH is changing from one visit to the next you know it's not just because you tested later or earlier in the day from the last time. TSH tends to be at it's highest in the morning so they typically recommend getting it tested in the morning too. Just make sure though that they also test your Free T3, Free T4 and Reverse T3 as these are the actual thyroid hormones (TSH is a pituitary hormone- not a thyroid hormone). I don't think food really makes a difference in the results. The only thing is that if you take thyroid (especially T3) you should wait to take your meds until after your blood test b/c it can mess up the results. And most of us take our meds on an empty stomach so it can absorb better which requires waiting 2 hours after eating or 1 hour before eating. Since this is the case it can make it difficult to find the time in the morning to eat in between all of this so it just works out better to wait on eating until after the test.

Chel