TSH is the current gold standard for diagnosis of hypothyroidism but are the current TSH levels optimal and how do they relate to Hashimoto’s disease? An excellent paper out of China entitled, “Using Hashimoto thyroiditis as gold standard to determine the upper limit value of thyroid stimulating hormone in a Chinese cohort” has shed some light on this important question which looked at the upper limit of TSH levels in relation to Hashimoto’s disease and hypothyroidism.

The authors begin by stating that subclinical hypothyroidism is characterized by “normal” T4, T3, Free T4, and Free T3 with an elevated TSH. And these patients have an increased risk of cholesterol abnormalities, heart disease, mental illness, and pregnancy complications even though their symptoms are relatively mild.

The current upper limit for “normal” TSH is 4.0-5.0 mU/L but some authors have stated that it should be 2.5-3.0 mU/L. The National Academy of Clinical Biochemists (NACB) guidelines have stated that 95% of normal individuals have a TSH below 2.5 mU/L which tends to be the upper limit value used by functional medicine practitioners.

How was the study done?

A hefty study group of 2,856 individuals aged 20-60 were examined and tested for the study.

Blood tests included:

* Free T3

* Free T4

* TSH

* Thyroid peroxidase antibodies

* Thyroglobulin antibody

* Total cholesterol

* Triglycerides

* LDL cholesterol

* Fasting glucose

* Uric acid

* ALT (liver enzyme)

* Creatinine

* Carbon dioxide combining power

Participants were diagnosed with Hashimoto’s disease based on the presence of thyroid antibodies and abnormalities on a thyroid ultrasound.

They excluded individuals who were taking thyroid medication, pregnant, history of thyroid operations, or a history of autoimmune disease. The average age was 36 with 75% being women and 25% men.

What were the study results?

7% of the subjects were diagnosed with Hashimoto’s disease with 14 men and 173 females which syncs with previous data that Hashimoto’s disease is more prevalent in women.

Those diagnosed with Hashimoto’s disease did not show any differences in age, body mass index, waist to hip ratio, blood pressure, liver tests, blood glucose, or cholesterol. Creatinine and uric acid levels were lower in the Hashimoto’s disease group but his is due to the higher prevalence of women in this group who tend to have lower levels of these markers compared to men.

The proportion of participants with Hashimoto’s disease was 4% when the TSH was below 2.6 compared to 14% when the TSH was above 2.6. They grouped the participants into three categories of 2.6, 2.9 and 4.5 TSH cutoff values and found some interesting results.

TSH values of 2.6 and 2.9 cutoff values were able to detect more people with abnormal triglycerides and LDL cholesterol. The authors did find that a TSH value of 4.2 to the be the upper limit of normal in their analysis.

However, the authors used a “prevalence of Hashimoto’s thyroiditis” ...