There is possibility of Thyroid Cancer that should be ruled out with ultrasound and biopsy. If you have lump on your thyroid - run as fast as you can.

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Could you tell me more about where you found out about there being a different ideal range for those on thyroxine? This is the first time I've heard this (22+ yrs on thyroxine.) All my many doctors have gone by the 0.4 - 4 range. Very curious. More on reddit.com

Quick clarification, ideal range for most people is between 1 and 2, not below 1. Below 1 is getting kinda close to being hyperthyroid, once it’s under 0.5 or 0.4 (depending on the chart you reference) it is hyperthyroid. Normal range is a screening tool to spot trouble in the general population. People who might just be ignoring symptoms get flagged for further screening when they are outside that range on screening tests. People who don’t have thyroid problems and take medication will make thyroid hormones on demand as needed. When they need more, their pituitaries will respond and make TSH to tell the thyroid it should be making some. TSH is the hormone that the pituitary makes to talk to the thyroid, and it’s going to vary, but in the normal range is about where it should be most of the time. Ideal range (1-2,) is the pituitary saying to the thyroid “yeah, right about there, that’s good.” At ideal the thyroid is fairly relaxed. Above the ideal range but still normal (2-4.5) is the thyroid saying “hey, I’d like some more of that please.” Below ideal but still normal (0.5-1) is the pituitary saying “that’s a bit much, easy off a little.” There are two levels of above normal range. Subclinical (4.5-10) is the pituitary screaming at the thyroid “HEY, pick up the pace lazy bones.” Occasionally, it’s just a moment when the body needed a bit extra, but often it is because the thyroid is having trouble keeping up, so it needs to be investigated further with more testing. Clinical (>10) is basically the pituitary screaming “HELP! HELP! HELP! HELP!” Below normal range (<0.5,) is the pituitary saying “enough, please stop.” Since we use medication to provide part or all of our thyroid needs, the pituitary should mostly be telling our thyroids that it is making just about the right amount, only asking for a wee bit more or a wee bit less occasionally. More on reddit.com

Your tsh is perfectly normal. Likely nothing is "slipping through the cracks" here, assuming all your other levels are good too. With your value specifically, it's quite near optimal. Standard range is set by the specific lab and is based on population studies of "normal" results. A large "normal" range doesn't make the test inaccurate or mean things are being missed. There's a lot of info out there on how these values are set, but basically normal is typically all within two standard deviations of the mean. So tsh range is not abnormally large. Coming from a lab tech, this isn't nearly as large of a range as most tests have. For a lot of things, like routine tests you see on a CBC for example, you can even be outside of normal range and still be fine. It's unlikely to be testing in normal range and have hypothyroidism. There's definitely no reason to be concerned that your life is on the line here. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5321289/ More on reddit.com