Heterophile Antibodies Can Cause False Thyroid Test Results

Causes for False Readings on Thyroid Tests

thyroid tests, blood tests, TSH test, thyroid stimulating hormone test

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With many conditions including thyroid disease, we look at laboratory values to direct treatment. Yet lab values can be in error for any number of reasons. With thyroid disease, the thyroid stimulating hormone (TSH) test has become the so-called gold standard test for evaluating thyroid function but is not always accurate. And treating your body based on a false reading can result in feeling poorly. Heterophile antibodies are thought to be one reason for a false reading on these tests. What should you know about lab errors and abnormal results?

Causes of Abnormal Test Results in General

While we often view lab tests as infallible given they provide us with concrete objective numbers, that's not always the case. In fact, based on probability alone you've likely had a test result or two that was inaccurate in your lifetime.

With thyroid tests, a significant cause is currently thought to be heterophile antibodies. Let's begin by discussing these antibodies, consider other possible reasons for abnormal tests, and then talk about what you can do and what you should know to be an advocate for your own health.

Heterophile Antibodies and False Thyroid Test Results

In 2011, an annual meeting of endocrinologists were informed that heterophile antibodies may pose a risk of erroneous results on TSH testing. Heterophile antibodies are also known as human anti-animal antibodies and are developed as a result of exposure to animal-derived pharmaceuticals and antibody therapies.

The developmental of heterophile antibodies is more common if you have received blood transfusions, vaccinations, or if you have been exposed to certain animals (not household pets).

It's not certain how common heterophile antibodies are, but estimates range from one percent up to 80 percent of the population. This wide discrepancy in prevalence is related to how the antibody is identified.

Recent Increase in the Prevalence of Heterophile Antibodies

Of note is that the presence of heterophile antibodies appears to have increased remarkably in 2010. In an abstract discussed at that meeting, it was found that 4.4 percent of hundreds of samples tested were affected by heterophile antibodies. Of more concern was that an abnormal TSH should lead to further testing, but that testing doesn't always happen. Therefore, the presence of these antibodies could have serious implications.

Impact of Heterophile Antibodies

The impact of heterophile antibodies may be very significant in that treatment decisions are frequently made based on the level of TSH. Symptoms are certainly considered, but the gold standard usually remains the TSH. What this means is that people living with thyroid disorders should be aware of this potential for abnormal results.

When to Suspect Heterophile Antibodies

Since TSH is the gold standard for making changes in thyroid medications, how can you know if you may have heterophile antibodies affecting your levels? It seems that a discrepancy between TSH and free T4 is the hallmark. Anyone who has symptoms inconsistent with their symptoms or unexpected based on their history or current dose of medication should have further testing.

Other Possible Causes of False Readings on Thyroid Tests

In addition to heterophile antibodies, there are many ways in which lab tests can give false readings ranging from errors in your blood draw to mix-ups in the lab, to errors in transcribing numbers. We know that medical errors are common, and a significant cause of illness and even death. It's likely that the terrifying headlines calling medical errors the third leading cause of death were flawed, but given that it was even considered is a red flag to be your own advocate and speak up if something doesn't seem right to you. For example, if you have symptoms of hyperthyroidism and your lab tests shows you are hypothyroid and vice versa. Sometimes the best thing to do is re-run a lab test, or request a different test which might reveal a discrepancy and indicate a possible error.

The Significance of the Problem May Be Overestimated

Though estimates of the presence of heterophile antibodies are considered to be increasing, the problem may not be as serious as first thought. Some laboratory specialists argue that most modern assays contain blocking antibodies that would eliminate the problem of an artificially high TSH. Until there is consensus what should you know?

What This Means For You

Knowing all of this, what can you do to be your own advocate in your thyroid disease care? Whether related to heterophile antibodies or some other form of lab error, talking to your physician if you don't feel well is paramount. If you've been treated for hypothyroidism for some time, you may have a grasp of how you feel if your medication dosage is too high or too low. If you aren't feeling right, make an appointment.

If you're being treated for hypothyroidism and have a TSH that comes back elevated (higher), it's likely that your physician would increase your dose of thyroid hormone replacement. If your elevated TSH levels are, however, due to the heterophile antibodies, this dosage increase could cause overdosage and medication-induced hyperthyroidism. On rare occasions, this has resulted in severe thyrotoxicosis (thyroid storm).

If you are feeling well on your replacement dosage, and you have a high TSH test result, you should ask your physician to also run ​Free T4 and Free T3 tests, to double-check whether they correlate with the elevated TSH level.

If You Do Not Have Thyroid Disease and Have an Elevated TSH

If you haven't been diagnosed with thyroid disease and have an elevated TSH, it could very well be that you have hypothyroidism. After all, thyroid disease is very common. At the same time, you may have heterophile antibodies causing the elevation and it could be a mistaken diagnosis.

If this happens to you, ask your physician to run free T4 and free T3 tests to confirm your diagnosis of hypothyroidism. Without this check, you could erroneously be diagnosed with hypothyroidism and started on treatment resulting in medication-induced hypothyroidism.

Bottom Line on Heterophile Antibodies and False TSH Tests

It's not clear how common heterophile antibodies are in the general population, but when present they can cause an erroneous high TSH level (on some assays but not others). Treating based on the TSH level alone may result in medication-induced hyperthyroidism for both those being treated for hypothyroidism and those mistakenly diagnosed with hypothyroidism based on the test.

If your TSH is elevated and you don't have symptoms of hypothyroidism (if you feel good) ask your physician to check a free T4 and free T3 level to correlate your numbers and look for discrepancies.

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