T3 is the active thyroid hormone utilized in the body. T3 can be used directly essentially everywhere in the body.
T4 is a storage form of thyroid hormones. T4 cannot be used anywhere in the body at all, so it is considered inactive or storage. It can only be converted to an active hormone state (T3) before being used.
Some T3 is made by the thyroid; the rest is converted from T4 in places like the liver and kidneys before being circulated for use around the body, also in cells that convert T4 to T3 for their own use directly.
T3 is also in a prescription called cytomel or liothyronine, this is synthetic T3. Cytomel is often sold in 5 mcg (low amount) or 25 mcg (high amount) pill forms so it is difficult to titrate a long term dosage sometimes if you need to be on it. T3 is also in natural thyroid (NDT) prescriptions (from animals). There are 9 mcg of T3 in each grain of natural thyroid in USA. T3 has very rapid effects. It has a fairly short half life.
T4 is in a prescription called Levothyroxine, Synthroid, Tirosint and other names. These are the synthetic forms. It also is in natural thyroid prescriptions (from animals). In natural thyroid there are 38 mcg of T4 per grain of natural thyroid (NDT) in USA. T4 tends to change things slowly because it is converted to T3 before being used, and may take weeks to come out of the body and thus has a longer half life.
T3 is best measured by Free t3 which is a measure of how much T3 is available for use. This varies fairly widely over the day. A higher value means more is available. A low value and we generally do poorly at that point of the day where it is low. There are other T3 measures other than the Free T3 form but they are not ideal. T3 labs don’t measure daytime levels well near time of taking medications based on experience, so Free t3 labs are fairly time sensitive. When Free t3 level is low, many of us experience severe hypo symptoms no matter what the TSH says. You can also experience too much T3 and get hyper symptoms so having an experienced physician handling prescriptions in the T3 or NDT area is ideal, unfortunately this is hard to find.
T4 is best measured using Free t4. When relatively high in some of us it excites a high level of hyper symptoms and I experience this fairly easily. I do poorly at high levels of Free t4. One can also be hypo or get hypo symptoms when the FT4 is quite low.
rT3: Reverse t3 is a primal response of our bodies sensing something wrong, and forcing a slowing of metabolic rates in an attempt to create a somewhat hidden self preservation mode of sorts. Basically your body attempts to slow metabolism when it senses you are ill, deficient in iron (ferritin), minerals, vitamins, other hormones, or otherwise have something off or wrong, or even you react in a negative way to the fillers in your thyroid hormone pills. Having a high metabolism when ill would not be a good thing in general, so we developed an internal system to slow metabolism at these times. Symptoms sometimes may include hair loss and fatigue not resolved by raising FT3 alone. Basically rT3 blocks T3 receptors all over the body and the Free t3 can't get in. So you will feel quite poor, sometimes even presenting with a good or very good FT3. rT3 looks similar to T3 to the body but it can't function like T3 at all. It blocks the active thyroid (T3) hormone from being used since receptors are blocked up by the rT3 molecule. We then expend less energy, but we won’t feel well. All people have rT3, one can never get rid of all of it. However when rT3 is really high, that is when our body has kicked into its mode of forcing a slowing metabolism. We can potentially correct situations of high rT3 by finding the source of the problem. rT3 is made from T4, and never comes from Free t3, or from cytomel, or any source of T3 in thyroid hormone pills such as DTE/NDT.
Simple version of rest of this blog
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Some generally good lab goals (USA lab type values) – reminder never take biotin the week of labs, biotin is in many supplements.
Total Vitamin D (25-Hydroxyvitamin D): 50 ng/mL
Good value on Ferritin: 50-80 ng/mL
B-12: 800 pg/mL (Best to use active B12 liquid drops if you opt to take any to raise)
Homocysteine: below 10
Folate - ideally some number like 6 or 7 ng/mL but at least below 10 is desired (not 14 or 22 or other huge number)
Selenium and Zinc can be tested to be sure if in normal range.
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If your Folate and/or homocysteine are above 10, have a look below at MTHFR section:
Lots of people with Thyca have problems in this area, one has a higher risk of Thyca if they have these MTHFR issues. It can cause other problems if you have it, so best to work on it if you can find help and/or help yourself with a doctor’s help.
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The rest of this is geared to somebody not doing great but one can adapt it as needed:
The general idea of T4 and T3 testing is finding the two problem areas (which are not about finding if you are out of the range), you can have both problems or just one of the two problems.
Too much T4 for you
Too little T3 for you.
Some of the problems listed below.
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When doing poorly and it is unresolved there is a kind of "from"
and "to" on where to go. But understand doing poorly differs greatly
by what kind of issues, symptoms and so on the individual can have with poorly
managed thyroid hormones. Also, some of the same type of issues can be had from
too much or too little (headache for example can be too much or too little),
and sometimes we can tell but most often it is difficult to tell which one is
dealing with: too much or too little, and of what thyroid hormone. Breaking it
into two area T4 and T3 helps plus knowing what is routine when you had a
thyroid, we can use the two as levers pushing each independently and some are
able to resolve the problems.
go "from":
A generally high, or at top of range, or somewhere above a moderate Free t4
(FT4). A result that is generally above when you had a thyroid, plus using TSH
alone to dose.
The basic goal is to have your doctor convert "to":
A good or a very good Free T3 (FT3), at light moderate to mid-level FT4 (like you
had when you had a thyroid) and Reverse t3 (RT3) as low as possible.
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A normal person who has a thyroid and is of an average lifestyle the Free T4 usually runs only about 1.0 - 1.2 or so assuming no exercise changes, stressors, other sudden factors right ahead of lab. Athletes and very active people may run higher (maybe 1.3 or 1.4), but sudden changes (exercise, dietary, stress, work, etc) ahead of labs heavily change the values when you have a thyroid. So sometimes it is hard to tell unless you remember what you were doing the week ahead of a lab in the past when you had a thyroid.
Some of us find returning to a kind of normal FT4 is half the key, the other half is getting that very good FT3. This is for people who do poorly, those who do great on T4 meds (symptom and issue free) don't need to worry about the details almost seems like. There are many other vitamin and filler/sensitivity issues too. Fillers in Synthroid are horrid for example to many of us (acacia with thyroid hormones is a bad combo for many of us). There is also ferritin/anemia and other medical issues which complicate things for some people. MTHFR with homocysteine labs testing above 10 (USA) or super elevated folate labs - these can cause issues for many as well.
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Good and bad looking labs example. We need labs with Free t4, Free t3 to see where we are, know when (time of day) you did labs plus it should not be right after taking thyroid meds.
Here is an example of a person that likely will have fewer issues, USA lab type values
Free t4: 1.09 ng/dL
Free t3: 3.72 pg/mL
Reverse T3: 10.8 ng/dl
An example of poor looking values or more likely to have issues.
Free t4: 1.8 ng/dL
Free t3: 2.4 pg/mL
Reverse T3: 29.4 ng/dl
Reasons that is bad looking data include but not limited to
Too much T4 for you = HYPER issues (see below for some examples), just way too much T4 for many of us
Too little T3 for you = HYPO issues (see below for some examples), just way too low a T3 level for many of us
Too much rT3 = makes it so you can't feel a decent FT3, so even if you get a good FT3 you might feel poorly. rT3 being relatively high can be from pill fillers, to poor iron/ferritin, anemia, to being sick, to just plain too much T4, to many other reasons.
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Two common problem areas and some symptoms often faced post TT
As thyroid cancer survivors, having no thyroid, we are fairly unique medically in that we can experience both an excess (hyper) and a deficiency (hypo) simultaneously.
HYPER (most common on pure T4 or large amounts of T4 versus any T3.
Basic summary: too high for you as an individual Free t4 (which is NOT
the listed range) ) symptoms include mood changes and swings, A mean
irritability or a short temper, headaches and migraines, anxiety,
palpitations & excess heart rate issues, shortness of breath and/or
breathlessness, sleeplessness/insomnia and restlessness, more of a sharp
body ache or pain like joint pain or sharp shoulder pain issues, too
fast a GI system (initially) or changes in GI system with eventual
constipation from dehydration in some cases, Pain type neuropathy,
weight changes due to excess hunger with little or no satiety, lots of
pre-migraine and migraine aura type effects (can include what I call
thyroid ocular aura disorders -TOADs or simply visual aura) even if you
never had migraines in your life.
HYPO (most common with low individual FT3 (does not mean below range)
even if TSH suppressed but can also be too low for you a Free t4) all the symptoms of hypothyroidism, but common
are fatigues, brain fog, depression, loss of attention span (forgetting
things), skin issues, hair loss and hair issues, fingernail issues,
too low a heart rate, feeling dog tired, Sleeping lots, slowing metabolic rate leading to
inability to lose weight despite honest effort, Tired irritability, more
of a dull and swollen body ache or pain like swollen joint pain, muscle
cramps, irritable/sensitive GI, inability to do things like we used to,
constipation or too slow a GI system, blooming allergies, just can't
focus on work or family. When very HYPO a differing kind of irritability
or a "tired irritability" and a differing headache than the HYPER one. A
very low Free T3 can also cause bradycardia, palpitations in some, and
many types of cardiac issues are possible. Many more issues are common
when HYPO and can be found on internet searches.
