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.”