Hypothyroidism, or low thyroid function, is one of the most common underlying chronic hormonal problem in the world. With around 20 million cases in America alone and 200 million people worldwide, hypothyroidism is a silent epidemic. What's worse is that around half of those struggling with this health problem are undiagnosed, and don't know why they feel the way they do.
Living with unexplained weight gain, fatigue, hair loss, brain fog, depression, anxiety or digestive problems can be debilitating and feel hopeless. If your thyroid isn't working well, nothing in your body works well. Many people will go to their doctor to have labs ran, suspecting it may be their thyroid. If your thyroid-stimulating hormone, or TSH, is out of the lab range, you're given Synthroid, or levothyroxine. If the labs are "normal," you're typically sent home, with no options left in mainstream medicine.
How Do We Get The "Normal" Lab Ranges?
If you still have low thyroid symptoms and your TSH is "normal," something is not being addressed. How do we get the "normal" lab range anyway? The reference range is based on a statistical average of the population of that lab. This is why, other than vitamin D and cholesterol levels, lab reference ranges will vary depending on the lab.
The people who typically have work done on labs — in other words, the population of that lab — are statistically not the healthiest segment of the population. So if the lab results are "normal" despite your having symptoms, what your doctor is essentially saying is you're just like a lot of other sick people.
In functional medicine, we look at a much narrower range where your body functions optimally and you feel great, in perfect health.
A Functional Medicine Guide To Understanding Your Thyroid Labs
A functional medicine look at your thyroid is more in depth than just a TSH and a T4. Here are some of the labs I run on my patients, what they actually mean, and where you want them to be:
Thyroid-stimulating hormone is released from your pituitary gland to communicate with your thyroid. If your TSH is high, it's sort of like your brain shouting at your thyroid to work more. Research has linked a lab "normal" TSH of 2.5-3.5 mIU/mL with a 69% risk of dying from a heart attack or stroke. Now you can see why the optimal "functional" range is so important for your health, not just looking for labs out of the larger reference range!
Lab Range: .45-5.5 mIU/L
Optimal Range: 1.8-2.5 mIU/L
T4 is mostly metabolically inactive in the body and has to be converted to T3 to be usable. This lab gives you a total of unbound and bound forms of T4. Hormones have to be unbound from the protein carrier to be used by your body. Because of this, this lab doesn't give us the activity of T4 when measured alone. T4 is best measured in conjunction with a T3 uptake.
Lab Range: 4.5-12 mg/DL
Optimal Range: 6.0-12.0 mg/DL
This lab doesn't look directly at T3, but is very useful at indirectly looking at other hormones such as estrogen or testosterone and their relation with the binding of thyroid hormones.
Reference Range: 22-35%
Optimal Range: 28%-38%
This lab shows us the total amount of the metabolically active thyroid hormone. It allows a doctor to check your body's ability to convert T4 to T3 and to rule out an overactive thyroid.
Lab Range: 80-200 ng/DL
Optimal Range: 100-180 ng/DL
This will tell you the levels of free or active form of T4. This will be low in cases of hypothyroidism but can be normal in subclinical, early stages of thyroid dysfunction.
Lab Range: 0.8-1.8 ng/DL
Optimal Range: 1.0-1.5 ng/DL
This is the more active, usable form of your thyroid hormone. Low T3 syndromes are a common dysfunction that I see in practice, and a low level of this hormone is strongly linked to a higher risk of heart attack. The problem with that if you're taking a synthetic T4 medication is that your body isn't converting the hormone properly into T3, though there are many reasons your thyroid medication may not be working.
Lab Range: 2.3-4.2 pg/mL
Optimal Range: 3.0-4.0 pg/mL
Chronic stress and high cortisol can raise levels of reverse T3, which is an unusable form of the thyroid hormone.
Reference Range: 8-25 ng/DL
Optimal Range: 9.2-24.1 ng/DL
High levels of thyroid antibodies shows an autoimmune attack against the thyroid. The overwhelming majority of low thyroid cases are on the autoimmune spectrum, the most common being Hashimoto's disease.
Thyroid Peroxidase (TPO) Ab Optimal Range: 0-15 IU/mL
Thyroglobulin Ab Optimal Range: 0-0.9 IU/mL
Additional labs to address your microbiome, immune system and other hormones should also be considered.
All of these labs will be a strong first step in finding out which thyroid pattern you have, and keep in mind there are many thyroid dysfunctions that typically don't show up on labs.