Hormone SERIES Thyroid 2 of 4: Thyroid Testing

As we discussed last week, the thyroid is the master regulator of our bodies. Since thyroid dysregulation can cause such a broad range of symptoms, it’s critical to adequately test to get a full picture of thyroid function. Today we’re going to take a deep dive into thyroid testing and its nuances.
 
There are many misunderstandings around thyroid testing. First, when testing for thyroid it’s important to run the right lab tests.
 
A single lab result is not the best way to assess your thyroid function.
 

Thyroid Testing

A full thyroid panel includes the following tests:

• TSH
• Free T4
• Free T3
• Reverse T3
• Thyroid antibodies

 
The thyroid antibodies can include an antithyroglobulin antibody, an anti-TPO (anti-thyroid peroxidase), and a TSI (thyroid-stimulating immunoglobulin).
 

Why Do Most Doctors Typically Only Test TSH?

Most providers only use TSH to screen for thyroid dysfunction. A single TSH is the best screening tool for hypothyroidism (underactive thyroid) or hyperthyroidism (overactive thyroid). The problem with using only this one test is that there is a broad range of thyroid functions in which people can have symptoms with “normal” function that is not optimal. This is also sometimes called subclinical hyper or hypothyroidism.
 
Also, some providers don’t address thyroid dysfunction if the patient doesn’t report clear symptoms. It is clear from the literature that there are many people who have a TSH that’s elevated and a T4 that’s low, but since they don’t have symptoms – or more likely they don’t have reported or obvious symptoms – they’re considered asymptomatic and their thyroid issues are ignored. I see this all the time.
 

A Note on Natural Thyroid Hormone Supplementation

I sometimes add in additional tests if the patient is on a natural thyroid hormone supplement. For these patients, additional tests might include:

• Total T4
• Total T3
• Thyroglobulin levels

 
Since natural thyroid hormones can suppress a TSH while having a normal T4 and T3, I am careful to check these to make sure I’m not overdosing the patient. I see this routinely and it’s so common, but I’ve learned not to get overly concerned about a low TSH in people on natural thyroid hormones as long as their total and free T4, T3, and thyroglobulin levels are balanced.
 

Normal vs. Optimal Ranges for Thyroid Labs

So what are the normal ranges for thyroid?
 
For TSH, the normal range is about 0.3 to 5.5. However, the optimal range is 0.3 to 2.
 
The normal range for free T3 is about 2.3 to 4.3, but the optimal range is 3.4 to 4.0.
 
The normal range for free T4 is 0.6 to 1.4 and the optimal range is 1.0 to 1.25.
 
A normal reverse T3 range is 8 to 25 but the optimal is 10 to 20.
 

A Sidenote on Reverse T3

Reverse T3 is typically not checked by endocrinologists and other specialists because of some of the nuances related to it. I think of the reverse T3 as the brakes. If reverse T3 is high, it’s blocking the function of free T3 so you can have a “normal” thyroid level but if your reverse T3 is high, you will still be symptomatic. In this case, the issue is not your thyroid but something at the level of the mitochondria in the cells that are causing your body to want to put on the brakes. This requires a deeper dive with a functional medicine specialist.
 

Summary

Gaining an understanding of these thyroid testing concepts will give you an amazing grasp of some of the nuances of thyroid labs. To see the big picture around the thyroid, it is important to run a full thyroid panel and consider optimal ranges, not just “normal” ranges.
 
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Take care and be well.
 
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