Thyroid Math: What Those Numbers Mean (and What Your Doc Probably Forgot to Tell You About Hypothyroidism)

You may have low thyroid function, also called HYPO-thyroidism, and not know it. But let’s face it… thyroid numbers are often counterintuitive and confusing. When you combine hypothyroidism with the common low-thyroid symptom of brain fog, maybe even a bit of depression, and you’ve got a perfect storm for feeling overwhelmed, and even worse, disempowered about what to do next. In this article, I will clear up the confusion about what the numbers mean when it comes to your thyroid.

Want a sampler of how confusing thyroid math can get?

– TSH goes up when thyroid function is low (TSH stands for Thyroid Stimulating Hormone).

– Your thyroid makes T1, T2, T3 and T4 but your mainstream doc will probably only check TSH, and maybe free T4.

– T3 is 4-fold more potent than T4, because T3 is the active form of thyroid hormone. Keep this in mind when changing doses (for instance, prescription T3 at a dose of 25 micrograms = T4 at a dose of 100 micrograms)

– Natural Dessicated Thyroid? 1 grain of Armour Thyroid is the same as 60 mg, which consists of T3 at 9 mcg together with 36 mcg of T4. Naturethroid? Oh, Jeez! ! One grain is 65 mg… and oh my gosh, you get the picture!

Here’s the math I most want you to know:

Thyroid Math - What Those Stats Mean (and What Your Doc Probably Forgot)1. In 2002, the American Association for Clinical Chemistry (AACC) lowered the normal range for TSH to 0.3-2.5. Most docs don’t know this and are still using the old, pre-2002 range! Laboratories too. AACC  reported that: “In the future, it is likely that the upper limit of the serum TSH euthyroid reference range will be reduced to 2.5 mIU/L because 95% of rigorously screened normal euthyroid volunteers have serum TSH values between 0.4 and 2.5 mIU/L.” They also stated that “a serum TSH result between 0.5 and 2.0 mIU/L is generally considered the therapeutic target for a standard L-T4 replacement dose for primary hypothyroidism.” (Quotes from Mary Shomon’s website – thank you, Mary, for your awesome advocacy!)

2. Many folks are thyroid resistant, defined by a high reverse T3 and low free T3. But the tricky part is getting the units lined up and interpreting the free T3: reverse T3 ratio properly. Here’s how you know – use this calculator right here.

3. Broadening the lab diagnostic criteria to thyroid levels above 3 would mean that  suggests that more than 13 million Americans are likely to be defined as hypothyroid. That’s a lot of people!

4. Keep your free T3 in the top half of the normal range, and TSH in the lower half of the normal range, and all is good. Bonus prixe if you keep your reverse T3 in the lower half of the normal range!

5. Women are 10 times more likely to have thyroid problems than men, which is part of the reason that thyroid often gets overlooked or dismissed!

6. If you have the triad of weight gain, fatigue and depression–think thyropause. It’s a common cause of these symptoms especially for women starting in their 40s.

I consider personal power to be defined in this way:

You are fully able to understand, create, express and communicate effectively your intentions: for your mind, body, thyroid, relationships, work, finances, and _______ (fill in the blank). You are powerful when you get what you intend.

Let’s start with feeling your power around the thyroid. I intend for you to feel:

– Ease around your weight
– Overflow of energy to meet your daily challenges
– Stable, supportive mood
– Content and serene
– Like your hair is staying where it belongs: on your head, in your eyebrows and not in your shower drain.

Are you feeling it?


  1. Kelly on February 1, 2012 at 6:34 pm

    I was diagnosed hypothyroid after my 2nd daughter was born in 2001, but was taken off of synthroid after my thyroid levels came back into normal range. I am now in my early 40’s and I have felt like I have been experiencing mild hypothyroid symptoms for the past year. My GP recently tested TSH (.783 uIU/mL), Free T4 (1.31 (ng/dL), and Free T3 (2.6 pg/mL). She felt everything was fine with my thyroid and is treating me with Adrenal Complex supplements for possible adrenal fatigue. Would it be beneficial to also ask her to test reverse T3 at this time? I have one kidney (due to nephrectomy in 2002) and also have low Vitamin D (4 ng/mL) down from 28.1 ng/mL back in June 2011 even after taking 2000 iu Vitamin D3 daily for the past 7 months. There doesn’t seem to be many doctors that specialize in this here in Reno, NV

  2. Jennifer on April 23, 2012 at 5:36 pm

    Hi Dr. Sara!
    Saw your blog so I hope you don’t mind a question? My doctor is out of town for the next month and my lab results for my thyroid came in. I’m dying to know an answer!
    My free T3 is 2.65 and my rT3 is 208.0. I calculated my ratio to be 12.7. I read somewhere that a healthy ratio would be above 20. Is this true? Would my numbers indicate that I am in fact hypothyroid?
    Any feedback you can give would be greatly appreciated! My TPO was negative at 10.1. Not sure if that’s a good or bad thing at this point!
    Thanks and God Bless you!