Optimal vs Normal Thyroid Levels for All Lab Tests & Ages
Do you have the feeling that your thyroid hormones may not be optimal even though they are normal?
Does it make sense to you that each person might have a different optimal level?
Or that maybe your genetics are playing a role in your thyroid function?
If you answered yes then this article is for you!
In it we will explore the idea of "normal thyroid levels" and "optimal thyroid levels" and how using the latter may help you feel better and reduce your symptoms.
Let's jump in:
The Difference Between "Optimal" and "Normal"
Thyroid hormones, like other hormones in the body, exist on a spectrum.
What this means is that your thyroid levels are not "black and white".
The amount of thyroid hormone that you need differs from the amount of thyroid hormone that someone else needs.
So why do Doctors insist on following the reference ranges given by labs?
To understand this you must understand how labs create these reference ranges.
This is also the reason that each lab has different values for their tests!
The actual lab values differ among populations, locations, and ethnicities.
So how can we take something so complex and boil it down to simple reference range endocrinology?
The practice of medicine that is relegated to numbers rather than symptoms and the clinical picture of the patient?
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Part of the reason has to do with how complex it would be to find the "perfect" dose for each patient, but just because it's difficult doesn't mean it shouldn't be attempted.
Because of the way that lab values are created we have a situation in which there are two ways to look at thyroid hormone in the serum (this applies to all hormones).
The first is to compare your specific values to that of the standard reference range.
In this approach, you are simply looking at the value of your thyroid lab tests and determining if they fall within the large range provided.
If you fall within the range then you are considered "good" and no more treatment is required.
This practice is known as reference range endocrinology and is a way to standardize hormone therapy.
This is also the same approach that MOST Doctors use when analyzing hormone levels and thyroid levels.
A second approach, and perhaps a better approach for many people, is to look at the value within the reference range and compare this value to the clinical picture of the patient.
If the value is in the low end of the reference range then perhaps it's worth considering that even though the value is technically normal that it may not be normal for that person, especially in the face of abnormal symptoms.
Consider this example:
This gradual decline (which occurs with many hormones) should change how Doctors look at the testosterone levels based on the age of the patient.
A 50-year-old man should (and will) have different testosterone levels than a 20-year-old man.
You would think that this would be obvious, but the reference range is the same for ALL men older than 18 and up into their 80's.
So, using this approach, a Testosterone level of 200 in a 50-year-old is no more concerning than a testosterone level of 200 in a 20-year-old because technically they both fall within the "normal range".
Obviously, the testosterone level of 200 is MORE concerning to the younger patient because this is a time when testosterone should be near the PEAK.
The bottom line?
Using a combination of age AND the clinical picture will allow for tighter control of hormone replacement therapy.
This same logic should apply when evaluating and treating thyroid dysfunction.
By altering the way that we look at the absolute values of thyroid hormones we can create a "normal range" but also an "optimal range".
This optimal range represents the ideal range that would be seen in an active, healthy adult without any medical conditions or metabolic issues.
And this is the range that you want to aim for - not the generic range created through statistical analysis of the population surrounding you.
The optimal range isn't perfect, but it will allow you to better understand why you may not feel well despite having so-called "normal" thyroid lab tests.
If you are symptomatic (meaning you have fatigue, weight gain, cold intolerance and so on) then you should compare your actual lab tests to the "optimal ranges" provided below:
Complete Lab Test
Abbreviation (Commonly referred to as)
Normal Range (Reference range on labs)
Optimal Range (Based on healthy adults)
Thyroid stimulating hormone
0.450 - 4.500 uIU/mL
0.5 - 1.0 uIU/mL
Free T3, Triiodothyronine
2.0 - 4.4 pg/mL
3.8 - 4.4 pg/mL
Free T4, Thyroxine
0.82 - 1.77 ng/dL
1.4 - 1.77 ng/dL
Reverse T3, Reverse Triiodothyronine
9.2 - 24.1 ng/dL
Less than 15.0 ng/dL
Total T3, Total Triiodothyronine
71 - 180 ng/dL
150 - 180 ng/dL
0.0 - 0.9 IU/mL
Thyroid Peroxidase Antibody
0 - 34 IU/mL
Note that each lab test has slightly different reference ranges but you can use the optimal ranges above to give you an idea that you can then apply to other lab companies and their reference ranges.
The reference ranges and units listed above are generated from LabCorp which is a lab testing company common in the United States.
If you compare your lab results to the reference range vs the optimal range you will notice that the optimal range is really just a "tighter" version of the reference range.
The standard reference range is much larger and it has to be to encompass a wide variety of ages that are used when it is created.
Thyroid Lab Tests Available
Beyond simply using the table above to compare your results to, it's often better to actually understand what is being tested and what it means in a larger sense.
Understanding what thyroid lab tests mean will help you understand what tests you
This is important because many physicians will not order a complete thyroid lab panel and instead will focus only on 1-2 standard tests.
Ordering a more expansive panel is often better, at least initially, because it can help identify common patterns of thyroid disease seen in various conditions.
Some conditions, such as obesity, cause only slight dysfunction in thyroid hormone which can be missed unless certain tests such as Reverse T3 are ordered.
Other conditions, such as Hashimoto's thyroiditis, may be missed if thyroid antibodies are not ordered.
Because of this, you should also have a basic understanding of the most common patterns of thyroid disease, some of which are outlined below:
Thyroid Antibodies (TPOab & TGab)
High (greater than 2.0)
Low (usually bottom 20-30% of the reference range)
May fluctuate over time but often normal
Low (usually bottom 20-30% of the reference range)
Low (very close to 0)
T3 is high, FT4 may be low
Normal (TSI may be elevated (3))
Low to Normal
High (usually higher than 20.0)
Low to Normal
This table doesn't include ALL patterns, but it should work to give you a general idea of how to evaluate thyroid lab tests.
With this table in mind let's discuss what each lab test means:
- TSH - TSH tests pituitary function and can be used to diagnose thyroid disease.
- Free T3 - Free T3 may be the most important measure of thyroid function in the serum because it measures the free and active thyroid hormone. T3 is more biologically active than T4.
- Free T4 - Free T4 measures the amount of free T4 in circulation. In order to be activated, T4 must turn into T3 so T4.
- Total T3 - Total T3 includes measurement of bound T3. Bound T3 is not considered active like free T3 but total T3 gives you a more stable long-term marker of T3 in circulation.
- Thyroid Antibodies - The thyroid antibodies include thyroglobulin antibody, thyroid peroxidase antibody and thyroid stimulating immunoglobulin. The presence of these antibodies in your serum may indicate an autoimmune disease which is damaging your thyroid gland.
- Reverse T3 - Reverse T3 helps measure the conversion capacity of your thyroid gland. High reverse T3 may be a sign that your body is having trouble converting T4 into the active thyroid hormone T3. High reverse T3 is commonly seen after rapid weight loss, in obesity, and in euthyroid sick syndrome (5).
You can learn more about each test in the links above.
Understanding TSH and the Controversy Surrounding this Test
TSH stands for Thyroid Stimulating Hormone and may be the most common thyroid test ordered.
TSH is a measure of pituitary function which is a gland in the brain.
Under normal circumstances, your body produces TSH which then tells the thyroid gland to produce thyroid hormone.
A high TSH is often a sign of hypothyroidism or inactive thyroid gland function while a low TSH is often a sign of hyperthyroidism or excessive thyroid gland function.
This can be confusing because intuitively it would seem that if there is a high amount of TSH being produced that there would also be a high amount of thyroid hormone being produced.
After all, TSH does have the name STIMULATING in it!
But this isn't the case because in order for TSH to be effective the thyroid gland must be working.
So even if TSH is high, if the thyroid gland can't produce thyroid hormone (because of inflammation or damage) and therefore thyroid hormone production will be impaired.
If this is confusing to you, don't worry!
You can just stick to the table above or look at the optimal ranges to help you understand if your TSH is in the right place.
TSH is often very helpful during the initial diagnosis of thyroid disease but tends to lack value after starting medication.
The reason for this has to do with how important free thyroid hormone levels for managing symptoms.
A so-called normal TSH ranges from 0.45 to 4.5 but newer studies have emerged which suggest a tighter range is likely necessary (6).
This newer range indicates that any TSH over 2.0-2.5 is likely abnormal and an early sign of thyroid disease (7).
When you are being treated with thyroid hormone a TSH of 0.5 to 1.0 is probably the ideal goal to shoot for as it more closely mimics the range of healthy adults (8).
Thyroid Testing by Age & Other Factors
Optimal lab ranges may vary based on metabolic capacity, thyroid conversion and the genetics of the individual.
Compared to other hormones in the body it looks like thyroid hormone is one hormone that really shouldn't diminish with age.
What do I mean?
This is actually uncommon when compared to other hormones such as estrogen/progesterone in women and testosterone in men (both which show a dramatic decline as we age).
Part of the reason that thyroid hormone may be preserved overage is that of its importance in metabolic function and determining the metabolism of the body.
Even though thyroid hormones shouldn't decline with age we do see a general increase in the incidence and risk of thyroid disease in people as they age (10).
This means that you have a much higher risk of developing thyroid disease (including hypothyroidism, hyperthyroidism and thyroid cancer) the older you get.
We also know that older individuals tend to become more sensitive to thyroid hormone medications.
This can create a tricky situation in which replacing thyroid hormone is necessary, but it can be difficult due to symptoms that may occur with this therapy.
Even though it's difficult it's still very important to maintain normal thyroid hormone levels throughout your life!
In fact, this approach to treatment is considered to fall into the category of "anti-aging" because the whole goal is to return hormonal levels to a more youthful pattern.
Thyroid hormone, much like the other sex hormones, plays a critical role in the regulation of important factors such as metabolism and body weight.
For this reason, it's important to properly identify and treat thyroid disease regardless of your age.
Bottom Line: "Optimal" thyroid hormone levels do not change with age, but as you age you may be at higher risk of developing thyroid problems. This should be compared to other sex hormones which do decline with age.
Thyroid Lab Tests During Pregnancy
During pregnancy, the best marker of thyroid status may be the measurement of free thyroid hormones such as Free T3 and Free T4.
TSH becomes less helpful because the placenta secretes hormones such as human chorionic gonadotropin, chorionic thyrotrophin, and molar thyrotrophin (13).
Pregnant and lactating women have an increased demand for thyroid function in the body.
During fetal development, the thyroid gland from the fetus takes up and produces thyroid hormone which is critical for normal development.
This means that proper iodine intake is required for pregnant women due to this increased demand!
This also means if you are pregnant and taking thyroid medication you may need to have your dose adjusted.
When you are taking thyroid medication, prior to pregnancy, your body may become dependent on the dose of thyroid medication that you are currently taking.
When this occurs your body is incapable of producing thyroid hormone naturally.
This means that your body can't naturally increase the amount of thyroid hormone that your body needs once you become pregnant.
Because of this, you need to have your thyroid dose adjusted as SOON as you become pregnant.
So if you were taking 50mcg of Synthroid prior to pregnancy, you may need up to 100mcg of Synthroid while you are actively pregnant.
It's also worth pointing out that thyroid lab tests become less valuable during pregnancy as well.
Due to changes in thyroid hormone activity the standard and even "optimal" reference ranges become less helpful.
Because of this, you will need to pay close attention to your symptoms during pregnancy and monitor closely for the signs and symptoms of hypothyroidism during this critical time.
Symptoms such as rapid weight gain, crushing fatigue, hair loss, constipation and so on may be early indicators that you are getting insufficient thyroid hormone.
When it comes to hormones it's often best to consider "optimal ranges" as opposed to "normal" ranges.
The reason for this is that each person has differing baseline hormone levels which means that the dose and optimal range for you will be different than other individuals.
If you are undergoing thyroid hormone replacement therapy you will often find superior results (as evidenced by more weight loss and reduced symptoms) when you take this approach.
In addition, watch out for other physiologic conditions that may alter the amount of thyroid hormone that your body needs!
Highly stressful situations, age and even pregnancy may all alter these references ranges and may alter the amount of thyroid hormone that you need day to day.
Now I want to hear from you:
Do you understand the difference between normal and optimal?
Are you having trouble getting your levels into the perfect range?
Do you have a doctor willing to work with you?
Leave your comments below!
References (Click to Expand)