TSH and free hormones: TSH is a reasonable screening test but does not tell you about actual free hormone levels. If TSH is abnormal, free thyroid hormones confirm whether there is a real thyroid problem.
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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.
Picking up post #30: that is the part I would want checked first.
A single value outside interval: usually uninformative on a single draw. What makes a result interesting: a trend across multiple draws, a magnitude well beyond the interval, a pattern that coheres with other values, or symptoms that fit.
1 like 7mo
LJankowiak, post #13: TSH and free hormones: TSH is a reasonable screening test but does not tell you about actual free hormone levels. If TSH is abnormal, free thyroid hormones confirm whether there is a real thyroid problem. Go to post
Coming back to post #32, because the follow-up matters more than the original answer.
Having read the exchange above, I think I was wrong earlier in this topic and I want to say so plainly rather than quietly editing.
The correction was fair and I had been repeating something I had not checked carefully enough.
new_here_2026, post #21: 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. Go to post
post #34 is right about the mechanism and I think understates the practical bit.
HbA1c and glucose: HbA1c reflects average glucose over months; a spot glucose measurement reflects the moment. Trending glucose downward while HbA1c stays flat is a different picture than glucose going up with HbA1c.
Thank you for the correction. I have edited my earlier post with a note rather than silently, so the thread still makes sense to read. The error was mine and it was the kind that comes from remembering a figure instead of looking it up.
3 likes 6mo
I read post #36 twice before replying, because I had assumed the opposite.
Renal function markers: eGFR is estimated, not measured. It depends on creatinine, age, and weight. A small change in creatinine might not mean a real change in kidney function.
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k.roos, post #35: post #34 is right about the mechanism and I think understates the practical bit. HbA1c and glucose: HbA1c reflects average glucose over months; a spot glucose measurement reflects the moment. Trending glucose downward while HbA1c stays flat is a different picture than glucose going up with HbA1c. Go to post
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.
On post #36 — agreed on the reasoning, with one qualification.
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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c.rasmussen, post #20: TSH and free hormones: TSH is a reasonable screening test but does not tell you about actual free hormone levels. If TSH is abnormal, free thyroid hormones confirm whether there is a real thyroid problem. Go to post
Practical note that does not fit anywhere else. Whatever you conclude from this topic, write down what you did and when. The single most useful thing in your own records is not any individual result; it is that they are dated and consecutive.
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. Go to post
Analytical imprecision: any measurement has an error margin. A small difference in consecutive tests is usually measurement noise, not a real change. Knowing the imprecision helps distinguish noise from signal.
Picking up post #41: that is the part I would want checked first.
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.
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Worth separating two things that post #41 runs together.
HbA1c and glucose: HbA1c reflects average glucose over months; a spot glucose measurement reflects the moment. Trending glucose downward while HbA1c stays flat is a different picture than glucose going up with HbA1c.
17 likes 6mo
r.jhannsdttir, post #7: A single value outside interval: usually uninformative on a single draw. What makes a result interesting: a trend across multiple draws, a magnitude well beyond the interval, a pattern that coheres with other values, or symptoms that fit. Go to post
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.
LJankowiak, post #13: TSH and free hormones: TSH is a reasonable screening test but does not tell you about actual free hormone levels. If TSH is abnormal, free thyroid hormones confirm whether there is a real thyroid problem. Go to post
On post #45 — agreed on the reasoning, with one qualification.
TSH and free hormones: TSH is a reasonable screening test but does not tell you about actual free hormone levels. If TSH is abnormal, free thyroid hormones confirm whether there is a real thyroid problem.
post #49 answers the question as asked. The question underneath it is different.
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.
3 likes 5mo
Collapsed as off-topic by two members at trust level 3 or above
A single value outside interval: usually uninformative on a single draw. What makes a result interesting: a trend across multiple draws, a magnitude well beyond the interval, a pattern that coheres with other values, or symptoms that fit.
Practical note that does not fit anywhere else. Whatever you conclude from this topic, write down what you did and when. The single most useful thing in your own records is not any individual result; it is that they are dated and consecutive.
0 likes 5mo
aliquot_line, post #52: Practical note that does not fit anywhere else. Whatever you conclude from this topic, write down what you did and when. The single most useful thing in your own records is not any individual result; it is that they are dated and consecutive. Go to post
post #52 answers the question as asked. The question underneath it is different.
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.
a.norgaard, post #12: I read post #10 twice before replying, because I had assumed the opposite. Two things before anyone answers the substance. First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound. Go to post
On post #50 — agreed on the reasoning, with one qualification.
Renal function markers: eGFR is estimated, not measured. It depends on creatinine, age, and weight. A small change in creatinine might not mean a real change in kidney function.
I read post #54 twice before replying, because I had assumed the opposite.
Analytical imprecision: any measurement has an error margin. A small difference in consecutive tests is usually measurement noise, not a real change. Knowing the imprecision helps distinguish noise from signal.
0 likes 5mo
post #56 is right about the mechanism and I think understates the practical bit.
I disagree with the reply above, and I think the disagreement is substantive rather than terminological.
The distinction being drawn does not survive when you look at the published data for this specific question. I would be glad to be shown wrong on this, because the version I am arguing against is more convenient.
1 like 5mo
e.lokken, post #19: A single value outside interval: usually uninformative on a single draw. What makes a result interesting: a trend across multiple draws, a magnitude well beyond the interval, a pattern that coheres with other values, or symptoms that fit. Go to post
A single value outside interval: usually uninformative on a single draw. What makes a result interesting: a trend across multiple draws, a magnitude well beyond the interval, a pattern that coheres with other values, or symptoms that fit.
i.bakken, post #38: I read post #36 twice before replying, because I had assumed the opposite. Renal function markers: eGFR is estimated, not measured. It depends on creatinine, age, and weight. A small change in creatinine might not mean a real change in kidney function. Go to post
Picking up post #56: that is the part I would want checked first.
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.
Coming back to post #58, because the follow-up matters more than the original answer.
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.
0 likes 5mo