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Frequently Asked Questions About Subclinical Hypothyroidism
An Exploration of Low-Level, Subtle and Borderline Underactive Thyroid

by Mary Shomon

What is Subclinical Hypothyroidism?

The medical definition of subclinical hypothyroidism is a hypothyroid condition -- usually asymptomatic -- in which free thyroxine (T4) is normal and thyroid stimulating hormone (TSH) level is between 5 and 25 mU/L, or, if a thyrotropin-releasing hormone (TRH) test is conducted, there's a greater than normal elevation in TSH response.

The reality is that, while the textbooks say and some doctors believe that TSH levels of 5 to 25 are not usually acompanied by symptoms, many patients actually suffer substantial symptoms at these levels. According to Dr. Douglas Ross, symptoms described in patients with subclinical hypothyroidism include greater than average incidence of problems with muscles and nerves, such as weakness, muscle fatigue, and tingling extremities.

And the level of 5 as a bottom "cutoff" is actually also being questioned.

In January of 2001, the American Association of Clinical Endocrinologists (AACE) released a statement that said: "Even though a TSH level between 3.0 and 5.0 uU/ml is in the normal range, it should be considered suspect since it may signal a case of evolving thyroid underactivity."

And some practitioners actually believe that levels above 2 are evidence of developing hypothyroidism.

In particular, there are practitioners who believe that a normal TSH level, with the presence of elevated thyroid antibodies, may trigger hypothyroidism symptoms, and may warrant treatment.

Elizabeth Vliet, MD, who runs the popular women's health centers, Her Place and who is author of the bestselling book, Screaming to be Heard: Hormonal Connections Women Suspect...and Doctors Ignore wrote in her book:

"The problem I have found is that too often women are told their thyroid is normal without having the complete thyroid tests done. Of course, what most people, and many physicians, don't realize is that...a 'normal range' on a laboratory report is just that: a range. A given person may require higher or lower levels to feel well and to function optimally. I think we must look at the lab results along with the clinical picture described by the patient...I have a series of more than a hundred patients, all but two are women, who had a normal TSH and turned out to have significantly elevated thyroid antibodies that meant they needed thyroid medication in order to feel normal. This type of oversight is particularly common with a type of thyroid disease called thyroiditis, which is about 25 times more common in females than males...a woman may experience the symptoms of disease months to years before TSH goes up..."
How Common is Subclinical Hypothyroidism?

Using the TSH of 5 as a bottom cutoff, it's estimated that on average, approximtely 8 percent of women, and 4 percent of men are subclinically hypothyroid. The prevalence is much higher with age, and 15 percent of women over the age of 60 and 8 percent of men are subclinically hypothyroid.

Given the AACE's belief that TSH over 3 may be suspect, the number of people who may be subclinically hypothyroid is likely to be far greater than currently thought.

What are the Risks for and Symptoms of Subclinical Hypothyroidism

The risks for and symptoms of subclinical hypothyroidism are the same as for regular hypothyroidism.

What Are the Risks of Not Treating Subclinical Hypothyroidism?

The risks of untreated subclinical hypothyroidism include:
  • Increased risk of heart attack and atherosclerosis
  • Increased risk of elevated cholesterol and high triglycerides
  • Increased risk of depression, anxiety, and panic attacks
  • Increased risk of miscarriage.
  • Increased risk of developmental delays in infants born to mothers who were subclinically hypothyroid during pregnancy

Should Subclinical Hypothyroidism be Treated?

Most practitioners believe that most patients with subclinical hypothyroidism should be treated, because treatment can prevent further worsening of the hypothyroidism and further elevation of the TSH, may prevent growth of a goiter, and may help eliminate symptoms.

According to Robert D. Utiger, M.D., writing in "Health News," from the New England Journal of Medicine:
For people with subclinical hypothyroidism who have no symptoms, some clinicians believe that treatment is not needed unless, or until, symptoms or signs of hypothyroidism appear. Others argue that even people free from symptoms should start thyroxine therapy in order to forestall the progression to overt hypothyroidism, which occurs in about 2 percent of people per year. Another pro-treatment argument is that some people with subclinical hypothyroidism have symptoms that will be improved by treatment, but that neither the person nor a physician or family members have detected them yet.

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All information is intended for your general knowledge only and is not a substitute for medical advice or treatment for specific medical conditions. You should seek prompt medical care for any specific health issues and consult your physician or health practitioner before starting a new treatment program. Please see our full disclaimer.