Whatever the answer on reference intervals turns out to be, the method for getting there is the same: state the assumption, do the arithmetic in public, invite the correction.
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Clinical · Bloodwork · continued
Reference intervals: how they are constructed and why one in twenty flags posts 31–60
This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
Post #30 is right about the mechanism and I think understates the practical bit.
Glycaemic markers integrate over different periods. A point glucose and a longer-term marker disagreeing is not a contradiction; it is two different questions.
The number is defensible. The precision I gave it is not.
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LJankowiak, post #13: An update on my earlier reference intervals post: the pattern held for another six weeks and then stopped, which I did not predict and cannot explain. Go to post
Coming back to post #32, because the follow-up matters more than the original answer.
Comparing results across laboratories is harder than it looks because reference intervals and methods differ. The same sample can produce different numbers and different flags.
new_here_2026, post #21: Repeat before acting is standard practice for an isolated abnormal result on most analytes, and it is standard for a reason. It cost nothing to check and would have cost something not to. Go to post
Taking post #34 at face value and following it one step further.
Reference intervals was covered in the wiki last year and the page has a review date on it, which is a better starting point than my memory of a thread.
The number people quote for reference intervals is a central estimate presented without its interval, and the interval is wide enough that the estimate is nearly uninformative on its own.
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I read post #37 twice before replying, because I had assumed the opposite.
Time of day: some biomarkers vary across the day. Cortisol in the morning differs from cortisol in the evening. Comparing results from different times of day is comparing things that are not the same.
I am confident about the direction and much less about the magnitude.
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k.roos, post #35: Taking post #34 at face value and following it one step further. Reference intervals was covered in the wiki last year and the page has a review date on it, which is a better starting point than my memory of a thread. Go to post
General information rather than advice about anyone's care. A single value outside a reference interval, on a single draw, in an otherwise unremarkable panel, is usually uninformative.
The disagreement above is smaller than it looks once the terms are fixed.
c.rasmussen, post #20: Time of day: some biomarkers vary across the day. Cortisol in the morning differs from cortisol in the evening. Comparing results from different times of day is comparing things that are not the same. A modest claim, modestly supported. Go to post
Bringing the actual numbers with intervals to an appointment is far more useful than describing them, and clinicians here consistently say so.
One case, stated as one case.
n.bridgewater, post #11: This follows post #8 rather than contradicting it. Liver enzymes: elevation does not specify cause. ALT and AST can rise from many things. Bilirubin helps narrow down the cause. Multiple markers together are more informative than one alone. Adding a source would improve this post and I do not have one to hand. Go to post
The most useful thing this subcategory does is help people tell an interesting result from an uninteresting one before booking an appointment about it.
Two claims get bundled together under reference intervals and they need separating. The descriptive one — this is what was observed — is usually well supported. The causal one — this is why — usually is not.
Almost every disagreement in threads like this one dissolves once you say which of the two you are making.
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Picking up post #41: that is the part I would want checked first.
On reference intervals, the part that usually goes wrong is that the question is asked as though it has one answer. It has a range, and the width of the range is the interesting bit.
If you can post the two or three numbers you are working from, several people here will check the arithmetic rather than argue about the conclusion.
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r.jhannsdttir, post #7: Filing a mild objection to the consensus on reference intervals. Mild because I might be wrong; an objection because nobody has addressed the case that does not fit. Go to post
A trend needs at least three points to be a trend. Two points are a line and a line through noise is still a line.
The short answer was in the first line; everything after is the working.
Reference intervals: constructed to contain the central 95% of a reference population, which means one in twenty healthy people falls outside one by definition. Add biological variation and analytical imprecision and the base rate of a meaningless flag is substantial.
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LJankowiak, post #13: An update on my earlier reference intervals post: the pattern held for another six weeks and then stopped, which I did not predict and cannot explain. Go to post
Everything in post #46 holds. The case it does not cover is the one I have.
Reference intervals would be much easier to settle if anyone reported the denominator. Almost nobody reports the denominator.
Narrowing post #49, because the general version has more than one answer.
Repeat before acting is standard practice for an isolated abnormal result on most analytes, and it is standard for a reason.
The variance between people here is larger than the effect being discussed.
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Two people in this thread mean different things by reference intervals and are disagreeing about the definition while believing they are disagreeing about the facts. Worth pausing to define it.
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aliquot_line, post #52: Two people in this thread mean different things by reference intervals and are disagreeing about the definition while believing they are disagreeing about the facts. Worth pausing to define it. Go to post
Thank you for taking the time. That was more work than a reply usually is.
a.norgaard, post #12: Worth separating two things that post #10 runs together. What I would tell a new member reading about reference intervals for the first time: the confident posts are not the reliable ones, and the reliable ones are longer. Go to post
Post #50 describes the usual case. This is about the unusual one.
Glycaemic markers integrate over different periods. A point glucose and a longer-term marker disagreeing is not a contradiction; it is two different questions.
Written quickly, so the reasoning may be tighter than the wording.
Biological variation: the person-to-person variation in a biomarker for a healthy person is larger than most people realize. Comparing your result to the reference interval is one thing; comparing your result today to your result from months ago is more sensitive to change.
I have written this out at length because the short version keeps being misread.
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I had written a reply contradicting post #54 and deleted it. Here is what survived.
Lipid panel interpretation: total, LDL, HDL, triglycerides all on one panel. Reading them together is more informative than reading one value in isolation. An elevated triglyceride with low HDL is different from triglyceride elevation alone.
Not a conclusion. A place to stand while looking for one.
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Picking up post #56: that is the part I would want checked first.
Reference intervals is well covered in the tag pages, and the older discussions are better than the recent ones because they were argued out properly. Worth twenty minutes before adding to this one.
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e.lokken, post #19: The most useful thing anyone has posted about reference intervals in this category was a table of what had been measured and by whom. That is what I would want again. Go to post
The reason reference intervals keeps being re-asked is that the answer is conditional and people quote it without the condition. It is not that the answer is unknown.
i.bakken, post #38: I read post #37 twice before replying, because I had assumed the opposite. Time of day: some biomarkers vary across the day. Cortisol in the morning differs from cortisol in the evening. Comparing results from different times of day is comparing things that are not the same. I am confident about the direction and much less about the… Go to post
Post #56 is right about the mechanism and I think understates the practical bit.
Glycaemic markers integrate over different periods. A point glucose and a longer-term marker disagreeing is not a contradiction; it is two different questions.
The part I am sure of is shorter than the part I have written.
Clear enough that I do not think I have a follow-up, which is unusual.
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