In 2001, Kim Rhyne gained 20 pounds in six weeks. Normally an energetic women’s ministry leader in Cleveland, she was suddenly so exhausted that she could barely drag herself out of bed. “I wasn’t eating a lot more or doing anything any differently than I had been before,” says Kim. “I had no idea what was going on with my body.”

Knowing that an underactive thyroid often causes these symptoms, Kim’s doctor gave her a blood test to check her thyroid function. When the results came back within the normal range—though just barely—he diagnosed her with depression and started her on antidepressants.

Nine months later and not feeling any better, Kim had her thyroid levels rechecked. This time her levels were higher, so her doctor diagnosed her with hypothyroidism and started her on the medication Synthroid, which is commonly used to treat the condition. The drug pushed her test results back into the normal range, but Kim still didn’t feel well. She even struggled to muster up the energy to go grocery shopping or chat with the congregants who frequently stopped by her home. “I would end up in bed before guests even left the house,” she recalls. Meanwhile, she was more irritable than ever, snapping at her husband for the littlest things.

Kim told her doctor how bad she was feeling but he wouldn’t raise her medication dosage, citing her normal test numbers. Then, earlier this year—nine years after she was first diagnosed—Kim started chatting with a woman at church who happened to be an endocrinologist (a doctor trained in the treatment of hormone disorders). The woman suggested that Kim come see her for a workup. Her findings: Kim needed a slightly higher dose of Synthroid. A few weeks later, Kim started to feel like her old self again. “I couldn’t believe that I had spent years feeling tired and irritated when the solution was as simple as taking a little more medication,” says Kim, now 41.

Unfortunately, Kim’s struggle to get the right treatment is not that uncommon. Nearly 13 million people in the U.S. are not correctly diagnosed with hypothyroidism, and experts think that the number is probably climbing. “One in eight Americans is now age 65 or over, and you’re more likely to develop thyroid problems when you get older,” explains E. Chester Ridgway, MD, a professor of medicine at the University of Colorado School of Medicine. “That 13 million may just be the tip of the iceberg,” he says.

Why are thyroid disorders so hard to detect? For one thing, doctors don’t agree on how to interpret screening tests. There are also several tests that check thyroid function, but many doctors use just one. And in some cases, like when test results are borderline “normal,” symptoms should be given extra weight when deciding on treatment.

One Test, Many Interpretations

Your thyroid gland plays a crucial role in regulating just about everything, including your heart rate, metabolism, muscles and mood. If your thyroid is underactive (hypothyroidism), it’s not making enough thyroid hormone, so your body starts pumping out extra thyroid-stimulating hormone (TSH), which makes your TSH levels high. Insufficient amounts of thyroid hormone can cause symptoms like weight gain, fatigue, chills, and dry skin, hair and nails. On the other hand, when your thyroid is making too much thyroid hormone, you’ve got an overactive thyroid (hyperthyroidism), which causes weight loss, insomnia and anxiety.

Although most experts agree that measuring TSH levels with a simple blood test is the best way to detect a thyroid issue, they differ on what should be considered normal. Most primary care doctors use one standard range (0.5 mIU/L to 5.0 mIU/L), but many endocrinologists narrow that range (0.3 mIU/L to 3.0 IU/L), meaning that a larger group of people fall outside it. Kim’s internist considered her TSH levels normal, but her endocrinologist found them high.

It’s also worth noting that the TSH screening isn’t the only one. Doctors can also test for antibodies that show up in Hashimoto’s disease, an autoimmune condition that causes up to 95% of all hypothyroidism cases. It’s possible to have normal TSH levels but high levels of these antibodies, says Theodore C. Friedman, MD, PhD, chief of endocrinology at Charles R. Drew University and a professor of medicine at UCLA. But not all doctors order this additional blood test. Some doctors also believe in measuring two forms of thyroid hormone (T3 and T4).

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