The Numbers That Actually Matter

The thyroid panel worth asking for is TSH, free T4, and thyroid antibodies, meaning TPO and, if your doctor will run it, thyroglobulin. Free T3 is worth raising and more contested than the internet admits. Book the draw early, take your medication after the needle rather than before, and stop any biotin supplement two days ahead, because it can make results wrong in both directions.

the second of eight letters about the years i spent solving my own thyroid. the first one is here, and it is where to start. please read the note at the bottom.

The year I was told I was fine

For a long stretch I was handed the same sentence at the end of every appointment. Your thyroid is normal. I would go home with the paper and the exhaustion, the two did not match, and I assumed the paper was right and I was the problem.

What I did not understand is that in most countries the first test is one test. Not a panel. One. That is a screening protocol rather than carelessness. But if your number sits inside the range while your body says otherwise, one number is where the conversation starts, not where it ends.

What each number is actually measuring

• TSH. Thyroid stimulating hormone, and the confusing part is that your thyroid does not make it. The pituitary does, and when it senses too little hormone it shouts louder, so TSH rises. A signal, not a measurement.
• Free T4. Thyroxine, what the thyroid mostly produces, largely a storage form. Free means the portion your body can actually use.
• Free T3. The active hormone, the one that does the work in your tissues, mostly converted from T4 elsewhere in the body.
• TPO antibodies. These do not measure function. They tell you whether your immune system is involved, a different and often more useful question.

The antibodies are the test I would not skip

Function tests tell you where your thyroid stands today. Antibodies suggest why. A raised TPO level points toward autoimmune thyroid disease, which is Hashimoto's, the most common cause of an underactive thyroid where iodine is sufficient. It is also why a result can read normal now and not stay that way.

Postpartum thyroiditis, where mine began, has a known association with these antibodies. Knowing would not have changed my treatment. It would have changed how seriously the tiredness was taken, including by me.

Free T3, and the honest version of that argument

Here I have to be careful, because this is where the internet is loudest and least reliable.

Free T3 is a real measurement. It is also true that most national guidelines do not recommend routine free T3 testing for an underactive thyroid, and that the evidence for adding T3 to standard levothyroxine is genuinely mixed rather than suppressed. Reverse T3 goes further, sold as the missing piece and not endorsed by mainstream endocrinology here, because it rises for reasons unrelated to the thyroid, including simply being unwell. So ask, as I did. Just walk in knowing it is a live debate rather than something your doctor is hiding.

Three things that can make a result wrong

• Biotin. It is in most hair, skin and nail supplements, so it is in a lot of our bathroom cabinets. It interferes with the immunoassay method many laboratories use and can push results falsely high or falsely low. Stop it a couple of days before a draw.
• The time of day. TSH peaks overnight and drifts down through the day, so an afternoon draw can read lower than a nine o'clock one. If you are tracking over months, keep the time consistent.
• Medication timing. Taking levothyroxine before the draw can lift measured T4 for hours. Blood first, tablet after.

What is worth testing at the same time

The exhaustion I blamed on my thyroid was not entirely my thyroid. Ferritin, vitamin D, B12 and folate all produce a tiredness identical from the inside, and they keep company with thyroid disease often enough that most doctors will add them if you ask.

How to ask, which turned out to matter

The sentence that finally worked was not a demand and not a list. It was this. I have been exhausted for months in a way rest does not fix, it started after a baby, and I want to understand whether my thyroid is part of it. Could we look at TSH, free T4 and antibodies rather than TSH alone.

A question, a reason, and the tests named. Doctors are not the obstacle. Ten minute appointments are.

Frequently asked questions

Which thyroid blood tests should I ask for?

Ask for TSH, free T4 and thyroid antibodies, meaning TPO and where available thyroglobulin. Many health systems screen with TSH alone and add free T4 only if that is abnormal, which is reasonable but can leave an autoimmune picture invisible. Free T3 is worth raising and remains debated.

Can you have a normal TSH and still have a thyroid problem?

Yes. A TSH inside the reference range can sit alongside raised thyroid antibodies, indicating autoimmune activity that may progress. Ranges are built from population data, so the far edge of normal may not be normal for one person. Exhaustion with normal results also has other causes, such as low iron.

Should I stop taking biotin before a thyroid blood test?

Biotin, present in many hair and nail supplements, interferes with the immunoassay methods many laboratories use and can produce falsely high or falsely low thyroid readings. Laboratories commonly advise pausing it for about two days before a draw, and telling whoever takes your blood.

What is the best time of day for a thyroid blood test?

Early morning. TSH peaks overnight and falls across the day, so an afternoon sample can read lower than a morning one from the same person. Keep the time consistent if you are comparing results over months, and if you take levothyroxine, give blood before that morning's dose.

What do TPO antibodies mean?

Thyroid peroxidase antibodies indicate the immune system is acting against the thyroid, pointing toward autoimmune thyroid disease, most often Hashimoto's. They describe cause rather than current function, so they can be raised while thyroid function tests still read normal. They are also associated with postpartum thyroiditis.

Next letter, exercise, inverted. Why heavy and slow did more for me than hot and fast, and where that stops being evidence and starts being my experience.

With love from Bali,
Myrah