Optimum Thyroid Labs--the New Normal

Is there such thing as an optimal lab number within the normal range for thyroid labs? Absolutely, yes.

Although there are small variations, most labs these days report the following as the normal range for thyroid labs:

• TSH: 0.5 – 4.5 uiu/mL
• free T4: 0.8 – 2.8 ng/dL
• free T3: 2.3 – 4.2 pg/mL

But is there are an optimal range within the these normal ranges? The answer is yes. Consider the following:

• A few years ago, TSH as high as 10 was considered normal. But today, a TSH above 4.5 would fit into the diagnosis of hypothyroidism or low thyroid function. Therefore, for many years, people with TSH between 4.5 – 10 were told that their thyroid function was “normal” even though by today’s standards, they would be hypothyroid. All those missed diagnoses and years of symptoms for undiagnosed and untreated patients. The trend over time has been the lowering of TSH in terms of what is considered “normal” and some labs now report that TSH above 3 or 3.5 is consistent with hypothyroidism. 

• Many endocrinologists today would treat a patient to a target TSH–usually between 0.5 and 2.5. For example, if a patient is diagnosed with hypothyroidism with a TSH of 6, the endocrinologist might start with a dose of thyroid medication at 0.05mg. If the follow-up labs show that TSH is now lowered to 4, the doctor might increase the dose to 0.07mg, and so on until the “target” TSH is achieved. A wise doctor would of course correlate the “target” TSH with the patient’s signs and symptoms. It is not always necessarily better to go for the lowest TSH. But if a patient has TSH of 3.0 but is still symptomatic, I personally would still dose up the patient to see if improvements can still be made. This approach may be called “treat to target.”

• For hypothyroid women who are preparing for pregnancy, the guidelines now indicate that the goal is to have a TSH of 2.5 or lower.  Many fertility doctors also now try to get TSH below 2.5 if they are helping sub-fertile women get pregnant. Therefore, many subspecialties such as obstetrics/gynecology and fertility medicine now recognize that TSH below 2.5 is the more optimal target, and not just a number “within the normal range.”

• Like TSH, there are also optimal numbers for free T4 and free T3 within the normal range. The ranges indicated in the chart above are based on some studies and clinical experience. I will admit that there is not a lot of comprehensive and solid evidence yet that we should always “treat to target” in terms of free T4 and T3. But evidence is emerging and this will get clarified over the years. HOWEVER, I want to point out that the concept of an optimal target is still very helpful clinically when it comes to free T4 and free T3. One example I can give is when you see a patient with normal/optimal TSH, but their free T4 or free T3, while within the normal range is on the cusp of becoming abnormally low. In these cases, you have to consider if maybe there is an issue with absorption with the medication, if the thyroid medication may be interacting with the other medication that the patient uses, or perhaps the patient because of genetics or some other factor, is not very good at converting the more inactive form of thyroid hormone to the active form. There are fixes to each of these scenarios (for example, adding T3-Cytomel if free T3 is abnormally low) and a good doctor who treats each patient patiently and individually will try to tailor-fit a treatment plan that will help address the patient’s signs and symptoms more adequately.

Take home messages:

• Within the normal range of common thyroid lab values, there is an optimal range.
• If a patient gets treatment for hypothyroidism, is within the normal range AND feels fine–then that’s wonder–continue the treatment and monitor regularly as we would with any patient who has a diagnosis.
• If a patient gets treatment for hypothyroidism, is within the normal range but outside the optimal range AND does NOT feel fine–my opinion is that there is a good argument that medication levels and/or the type and combination of medications (levothyroxine, cytomel. armour thyroid, compounded medication) should be adjusted to reach the optimal range.
• Do not let your doctors dismiss your questions about possibly adjusting thyroid medications if you are still feeling symptoms of hypothyroidism just because your labs are within the normal range….”so it must be something else.”  If the labs are not optimal, effort should be made to try to reach the optimal range.
• If the optimal range is reached, and you still feel symptoms…this is when I would say other possible causes of fatigue should be considered and addressed.