First test positive diagnosis- second test negative diagnosis? Help please!

Before anyone can answer your question, we'd have to see the complete set of lab results used to assay your thyroid function.

We'd also have to see the range of "normals" used in the lab that ran your thyroid assay.

It's possible that on one day, your results were inside the normal range, but on the 2nd day your results fell a little bit outside of the range.

I've assumed that the 2 assays were run by the same lab. If not, we can't compare the two sets of values for thyroid function.

Your internist can have the thyroid re-assayed.

This happened to me -- I had a test that showed I was in the abnormal range, but I was resistant to getting started on the medication (I forget the name but it's something you're supposed to take forever once you start) and wanted to try some other things first, especially exercise. I started exercising more seriously, was re-tested, and was in the normal range. (There isn't really a clear-cut negative or positive result, as I understand it -- just a range.)

This doesn't mean anything in particular -- especially, don't take it to mean that if you exercise you won't have any more problems. What it does mean though is that tests can and do vary. I'd recommend staying on top of it, seeing how you feel, and continuing to get tests. I've felt much better since the change to regular/ serious exercise so haven't felt a need to be re-retested (the last time was only about 6 months ago anyway). It's something I plan to revisit though.

Go ahead and keep the appt. with the endocrinologist and see what he/ she has to say.

Years ago, my sugar was running high. The doctor ordered a 2 hour glucose tolerence test. In this test you are given an obnoxiously sweet drink. They then check your blood every half hour for two hours to see how the insulin in your body processes the sugar.

It came out that I have diabetes. Since then, every regular glucose test that I have taken has come out in the high end of normal range. Go figure!

I'd go to the endocrinologist if I were you.

Hah! Me too. Might be subtle changes in life style, if you are using A1c readings as a guide.

I'd echo the suggestion that you see a specialist, if you can (and assuming you're not already).

The thyroid is tricky. Levels can read low if you're chronically stressed, or as the result of another disease (some of which may cause some symptoms that are similar to hypothyroidism). Levels fluctuate throughout the day, and "normal" levels can differ between individuals. It's tough to interpret, and I'd definitely want a boarded endocrinologist working on it.

Thanks everyone for your advice! I will definitely go see the specialist. The weird thing is about the two tests is that I had the first one done on Wednesday, and the Dr. said my thyroid is low. I had the second test done Thursday (the very next day) and he said it went up. I'm just confused how it can vary from one day to the next!

Every diagnostic assay has a certain level of variability associated with the test. It's known as the reproducibility of the assay and it indicates how the results of the same sample repeat over time. There are all sorts of things that affect the reproducibility of an assay. Generally, the variability of an assay is determined during clinical trials of the product before it goes on the market and is part of the information in the package insert of the test kit.

Reproducibility is calculated by taking the same sample and testing multiple replicates of that sample on a single run, on multiple runs each day, over multiple days, by multiple techs, in multiple labs, and on multiple lots of reagents. Any quantitative test (a test where the result is a number) has a known variability. It's possible that the two results you were given are within the known variability of the assay. It's also possible that there was a slight difference in the two samples you provided. I'd be more interested in the time of day they were drawn in relation to each other than the fact that it was Wednesday vs Thursday. The difference could very well be morning vs afternoon and how your thyroid function changes slightly throughout the day.

Yes, I would keep the appt with the endocrinologist. He'll probably suggest repeating the tests again to get a better feel for your current state and the suggestion to recheck the levels periodically will probably be repeated.

Good luck!


Phoenix and Roger --- that's a very common observation. Probably, as Roger says, to slight changes in lifestyle once the first diagnosis is made.

Have you had the A1C test?