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
- Thyroid peroxidase antibodies
- Thyroglobulin antibody
- Total cholesterol
- LDL cholesterol
- Fasting glucose
- Uric acid
- ALT (liver enzyme)
- 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” factor to determine the upper limit of TSH and found a range of 2.6-2.9 to be more appropriate. They state that this correlates with the National Academy of Clinical Biochemists findings of a 2.5 upper limit for TSH levels.
The authors reference multiple studies linking TSH levels in the upper limit to high blood pressure, high cholesterol, and a higher Framingham score which is a marker for cardiovascular disease risk. These include:
“This study shows a high prevalence of Hashimoto’s thyroiditis occurred among individuals with a TSH of 2.6-2.9 mU/L. These values are possible to be the “true” values of normal upper limit of TSH for Chinese population.”
Dr. Hedberg’s Comments
We have known for some time the flaws of the TSH test which leaves many patients misdiagnosed as normal despite their symptoms which are usually chalked up to be psychological issues and the patient is referred to a psychiatrist.
This study illustrates that individuals with a TSH above 2.5 should be screened for Hashimoto’s disease as well as cardiovascular risk markers. Hypothyroidism usually leads to abnormal cholesterol levels so patients may actually be put on statin medications to lower cholesterol despite the issue being primarly a thyroid issue. Doctors who utilize the current TSH range may be missing patients with early signs of hypothyroidism.
However, there are two sides the coin. Functional medicine practitioners can be just as negligent in their analyses by over-analyzing TSH levels and trying to force the patient’s TSH levels to a lower number despite how the patient is feeling. We treat patients not lab tests.
Additionally, there can be a lack of emphasis on other body systems that are connected to the thyroid such as gut health, stress, blood sugar, hormones as well as not knowing about the intimate connections between thyroid health and ferritin, zinc, diet, sleep, chronic infections etc.
Is it worse to put a patient on thyroid medication who doesn’t need it or to not put a patient on thyroid medication who does need it? They both have their detrimental effects so both conventional and functional medicine needs a thyroid makeover when it comes to thyroid management. And this goes for the use of T4/T3 combination therapy or the use of T3 alone which is rarely necessary but that is for another article.
The most important thing to understand is that we can’t rely soley on TSH values but we can use it as a guide for further investigation into Hashimoto’s disease and cardiovascular risk factors. The majority of the time we can successfully get a patient feeling well again without thyroid hormone by focusing on their overall health and balancing all the systems in their body.