Change in Dosage
The most obvious cause of a TSH change is a change in dosage.
But sometimes, the interaction between TSH and dosage changes can be confusing.
For example, you may remember your doctor saying “your thyroid is low” – and interpret that as meaning that you are hypothyroid. But the doctor may have said – or may have meant – “your TSH is low” – which is indicative of hyperthyroidism.
Remember, a low TSH is indicative of hyperthyroidism – an overactive thyroid – and a high TSH is indicative of hypothyroidism – an underactive thyroid. The body produces TSH as a messenger to tell the thyroid to “make more thyroid hormone.” So, when your thyroid is already over-producing, the TSH drops to low levels. And when you’re hypothyroid, your body keeps making more and more TSH to keep urging the thyroid into production.
So, if your TSH shows that it’s low, your doctor will possibly reduce your dosage of thyroid hormone replacement, so that the TSH will go up. And if TSH is high, your doctor will likely increase your dosage, so TSH drops.
Potency Fluctuations in Your Medicine
If you’ve had your prescription refilled since your last thyroid test, this may be a reason why your TSH has changed.
Thyroid drugs, for the most part, can fluctuate fairly significantly in terms of potency and stability, and yet still be sold. So, even from batch to batch of the same brand drug at the same dosage, filled by the same pharmacy, you may experience variance in the drug’s potency level, with significant enough potency changes to affect your TSH somewhat.
This situation is being partially remedied by the New Drug Application process going on for levothyroxine products (i.e., Synthroid), which will help ensure more consistent potency, and less fluctuations in potency.
One option is to consider looking into whether you can get larger quantities of pills – so that you get pills from a single batch, and don’t have to refill as often. Some insurance companies will actually encourage you to get three-month supplies, via their mail-order pharmacy services, so this might be a good option.
If you are on levothyroxine, you can ask your doctor whether you should try the only FDA-approved levothyroxines as of October 2001, Unithroid and Levoxyl.
Lab Changes or Mixups
Different laboratories may return slightly different results. If you have a variance from one test result to the next, be sure to check with your doctor to find out if the new test was sent to the same laboratory as the first test. If the samples went to a new lab, that may account for next test results are substantially different and are coming from a new lab, it’s worth retesting to confirm that the test results are accurate.
Sometimes there are simply errors in lab results. Samples are switched, numbers transcribed, etc. So if you get results that simply don’t make sense, don’t be afraid to ask the doctor to confirm with a retest.