I don't understand why the reference range for the particular laboratory analysing the blood is needed in interpreting a result for TSH/T4, etc.
e.g. "There is a range, which is used for the tests. These vary sometimes which is why you must always ask what the range is, so that you can see where you are in the range."
A range of what, exactly?
I thought a blood test result, e.g. TSH of 2, was an exact measurement of hormone level in that particular blood sample, and the reference range was just what the lab recommended a person's results should fall into.
If one needs the reference range, does that mean instead that a person's result is predicated as falling into a particular percentile of the population as calculated by the laboratory? In other words, if exactly the same blood sample was sent to ten different laboratories, you could get up to ten different results back?
Like, say, if you set an examination with 100 participants. You could either:
☻Give each student an exact mark, as in "Your score was 75%", or
☻You would look at the lowest mark scored and the highest mark scored and grade accordingly, so if the highest mark scored was 85% and the lowest was, say, 35%, you'd award scores between 75% and 85% Grade A, and those scoring 35% to 45% would be in the lowest grade, even though no-one scored zero.
How much does the "range" matter, particularly given they are so wide? I mean, if someone said to me, "My TSH is 1", I'd respond: "That sounds about okay, could perhaps be a tad lower: how do you feel?" But if they said "My FT4 is 1", I'd go: "Eek!".
I hope what I'm asking is clear. I've spent some time browsing through posts on reference ranges and ended up more confused than ever. Can someone please explain in very simple layman's terms? Many thanks.