People frequently write to ask about why they have different TSH levels from blood test to blood test. For example, a TSH test three months ago may have showed a TSH level of 3.0, but the most recent test this week shows 1.1. Or perhaps a year ago, the TSH was 0.5, and now it's 5.0.
What factors might account for a TSH that is changing? Are there things you may be doing that are affecting your TSH? Let's take a look at some of the factors that can cause your TSH to fluctuate.
1. 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.
2. 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.
3. 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.
4. Timing of When You Take Your Pill
If you are taking your pill at different times each day, you may be sometimes taking your thyroid hormone on an empty stomach, and sometimes with or after food. Taking thyroid hormone with food may delay or reduce the drug's absorption by changing the rate at which it dissolves, or by changing the stomach's acid balance. This means that, if you were taking your thyroid hormone on an empty stomach and start taking it with food, you may see an increase in TSH. And if you were taking it with food, and start taking it on an empty stomach, you may see a decrease in TSH.
If you want to get the most "bang for your buck," thyroid hormone-wise, you'll have best absorption if you take your thyroid hormone first thing the morning, on an empty stomach, about one hour before eating. But ultimately, consistency is what you should strive for, in terms of how you take your drugs. If you're going to take your thyroid hormone with food, take it every day with food, consistently. Don't take it some days with food, some days without, or you're likelier to have erratic absorption, and it may be harder to regulate your TSH levels.
And, if you plan to make a change from taking it one way to the other, it's advisable to get tested again a few weeks after you've settled into your new pattern, to see if you need a dosage adjustment.
5. Starting/Stopping a High-Fiber Diet
A high fiber diet can also affect your thyroid hormone absorption, and ultimately, your TSH level, because it affects digestion speed or speed of food absorption into the stomach, and can reduce the ability to absorb your medication somewhat. That doesn't mean you should stop eating high-fiber. Again, the key is consistency. If you are already eating a high-fiber diet regularly, and have regular TSH testing done, you shouldn't need to change your diet. If you are starting a new regimen of eating high-fiber foods, plan to get tested around six to eight weeks after you change your diet, to make sure you're receiving the proper amount of thyroid hormone. Don't change back and forth however, or you'll risk erratic absorption, and that can affect TSH levels and symptoms.
Again, to bypass much of the concern, you can take your thyroid hormone first thing in the morning, on an empty stomach, waiting at least an hour to eat. This will ensure maximum absorption.
6. Starting/Stopping Calcium or Iron Supplements
Many people -- in particular, women at risk of osteoporosis or anemia, and pregnant women -- take thyroid replacement along with supplemental calcium or iron. Researchers have found that taking thyroid hormone at the same time as calcium supplements can make less thyroid hormone available, and cause TSH to rise. Calcium should be taken at least four to twelve hours apart from the thyroid hormone can avoid this problem. Taking the calcium separately may still not be enough to prevent the calcium carbonate form of calcium from interfering with absorption, however, so you may wish to talk to your practitioner about taking another form of calcium supplementation if you are on calcium carbonate.
It is also known that taking iron tablets, or vitamins with iron -- such as prenatal vitamins -- at the same time as your thyroid hormone can make the thyroid hormone less effective. Many doctors recommend at least two to four hours between taking iron and the thyroid hormone.
What goes for calcium supplements also goes for calcium-fortified orange juice. With more manufacturers adding calcium to juices like orange or cranberry juice, remember that these juices act like supplements, so follow the above instructions regarding calcium.
7. Eating Too Many Soy Products
For people with autoimmune thyroid disease, overconsumption of soy products that are high in isoflavones may result in a higher TSH. If you're recently started taking an over-the-counter "menopause supplement," or soy protein powders, or other highly concentrated form of soy, you may find it aggravating your thyroid condition. Eating some soy foods are probably not a problem for many people, but if you've just started or stopped a soy-intensive diet or supplements, and are having trouble with TSH adjustment, you might investigate whether soy is the culprit.
8. Eating Too Many Goitrogenic Foods
Certain foods besides soy can also have what's known as a goitrogenic effect, or the ability to enlarge the thyroid and make it form a goiter. These foods can act like antithyroid drugs in disabling the thyroid, and causing hypothyroidism. If you still have a thyroid, you need to be more concerned about not overconsuming these goitrogens, particularly raw. What foods are goitrogenic? Brussels sprouts, rutabaga, turnips, kohlrabi, radishes, cauliflower, African cassava, millet, babassu (a palm-tree coconut fruit popular in Brazil and Africa) cabbage, and kale are all considered goitrogenic. Some experts believe that the enzymes involved in the formation of goitrogenic materials in plants can be destroyed by cooking, so thorough cooking may minimize some or most goitrogenic potential. Eating reasonable amounts of goitrogenic foods, raw or cooked, are probably not a problem for most people.
9. Change of Seasons
Many thyroid patients aren't aware that TSH can change along with the seasons. The research shows that TSH can naturally rise during colder months, and drop to low normal or even hyperthyroid levels in the warmest months. Some doctors will adjust for this by prescribing slightly increased dosages during colder months, and reducing dosage during warm periods. Most, however, are not aware of this seasonal fluctuation, leaving patients increasingly hypothyroid during cold months, or going through warmer months more hyperthyroid. This seasonal fluctuation can be more pronounced in older people, and in particularly cold climates.
10. Hormonal Fluctuations
Taking estrogen in any form, whether as hormone replacement therapy, or in birth control pills, can affect thyroid test results. For example, some women taking supplemental estrogen may need to take more thyroid replacement hormone. Estrogen increases a particular protein that binds thyroid hormone to it, making the thyroid hormone partially inactive. Thyroid tests can end up showing falsely increased total T-4 levels. For women without thyroids in particular, this can increase the dosage requirement slightly, as there is no thyroid to compensate.
Menopause, with its fluctuating hormone levels, can also impact your TSH levels.
The intense surge in estrogen during early pregnancy can increase your TSH, and increase your body's need for thyroid hormone. It's particularly important for a woman to have her TSH tested periodically in early pregnancy, to ensure that dosages can be modified accordingly. TSH will frequently drop after delivery as well, in response to these shifts.
12. Herbs/Supplements You Are Taking
Some herbal supplements can have an impact on thyroid function. Herbs such as the ayurvedic herb "guggul," and supplements such as tyrosine, and products containing iodine such as vitamins, or kelp and bladderwrack supplements have the potential to either increase or decrease thyroid function, and thus, TSH can fluctuate.
13. Prescription Drugs You Are Taking
Starting or stopping one of a number of prescription drugs can have an impact on your TSH.
Antidepressants -- Taking thyroid hormone replacement while taking the popular antidepressant sertraline -- brand name Zoloft -- can cause a decrease in the effectiveness of the thyroid hormone replacement, and make your TSH rise. This same effect has also been seen in patients receiving other selective serotonin-reuptake inhibitors such as Paxil (paroxetine) and Prozac (fluoxetine). If you are on an antidepressant or thyroid hormone and your doctor wants to prescribe the other, be sure to discuss these issues.
Cholesterol-Lowering Drugs Cholestyramine or Colestipol -- brand names such as Colestrol, Questran, Colestid -- can bind thyroid hormones. Many doctors recommend that a minimum of four to five hours should elapse between taking these drugs and thyroid hormones.
Corticosteroids/Adrenocorticosteroids -- brands include Cortisone, Cortistab and Cortone -- can suppress TSH, and can block conversion of T4 to T3 in some people.
This is by no means an inclusive list, so if you have TSH fluctuations and have started or stopped a drug in the interim period, be sure to discuss the entire list of drugs you are taking with your doctor, to make sure there are no interaction problems.
14. Stress and Illness
Your endocrine system is responsive to physical and emotional stress, and periods of intense stress, or the relief of such stress, may have an impact on your TSH levels. Some Graves' Disease patients report, for example, that they will have a drop in TSH levels, and require higher doses of antithyroid drugs, during and after periods when they are undergoing stress, not getting proper nutrition, or are overtired due to insufficient sleep. A similar effect can take place with Hashimoto's Disease patients who see TSH rise as a result of stressors.
15. Progression of Your Thyroid Disease
You may have been diagnosed with autoimmune Hashimoto's Disease a year ago, prescribed thyroid hormone, gone back six weeks later, and your TSH was 2.5. The doctor decided that your levels were fine, and told you to come back in a year. And now, this year's test shows your TSH at 5.7. This sort of increase may reflect the progression of the autoimmune process...in that as antibodies further attack the thyroid, it becomes less and less able to produce thyroid hormone on its own, therefore, TSH will rise. This same process works in the reverse with Graves' Disease, where the same dose of antithyroid drugs that kept you in the normal range six months ago is now leaving you still hyperthyroid, as the thyroid becomes even more overactive.
In addition, in the period post-pregnancy, you may have been diagnosed with a post-partum thyroid problem. For the majority of women, this condition will resolve itself, meaning that over time, you can expect the thyroid to attempt to return to normal, TSH levels will reflect these changes, and your drug dosages will need to be changed in response.