Clinical · Bloodwork · continued

Fasting versus non-fasting and which tests care posts 61–79

Clinical › Bloodwork eGFR & renal function lipase & amylase HbA1c Solved

This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1 · go to the accepted answer.

n.haddadTL2 Moderator2 Jul 2026 · edited#61

steady_state, post #51: 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

On post #57 — 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.

3 likes in reply to #51 25d

n.stanescuTL24 Jul 2026#62

Collapsed as off-topic by two members at trust level 3 or above

post #61 answers the question as asked. The question underneath it is different.

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.

j.mwangiTL4 Moderator5 Jul 2026#63

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.

31 likes 23d

s.kimaniTL2 Moderator7 Jul 2026#64

s.ivaturi, post #5: 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

Fasting state: some lab tests require fasting; others do not. Lipids on a fasting draw differ from lipids on a fed draw. Always note whether the test was fasting when comparing results.

16 likes in reply to #5 21d

s.cardosoTL2 Moderator8 Jul 2026#65

Worth separating two things that post #61 runs together.

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.

6 likes 20d

g.ibarraTL2 Moderator9 Jul 2026#66

e.ferreira, post #48: 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. Go to post

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.

1 like in reply to #48 18d

j.nwosuTL2 Moderator11 Jul 2026#67

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 17d

b.petrovTL2 Moderator12 Jul 2026#68

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.

22 likes 16d

ca.haddadTL2 Moderator14 Jul 2026#69

0 likes 14d

v.klausenTL3Regular15 Jul 2026 · edited#70

post #69 answers the question as asked. The question underneath it is different.

33 likes 13d

z.vogelTL2 Moderator16 Jul 2026#71

Picking up post #68: that is the part I would want checked first.

I disagree with the reply above, and I think the disagreement is substantive rather than terminological.

7 likes 12d

diluent_watchTL2Member18 Jul 2026#72

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.

17 likes 10d

ca.vermeulenTL2 Moderator19 Jul 2026#73

lc_gradient, post #39: 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

Fasting state: some lab tests require fasting; others do not. Lipids on a fasting draw differ from lipids on a fed draw. Always note whether the test was fasting when comparing results.

0 likes in reply to #39 9d

WoodhouseTL2Member20 Jul 2026#74

dietitian_hollis, post #55: 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

0 likes in reply to #55 8d

g.verhoevenTL2 Moderator22 Jul 2026#75

This follows post #72 rather than contradicting it.

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.

11 likes 6d

r.scholtenTL2Member23 Jul 2026#76

I read post #74 twice before replying, because I had assumed the opposite.

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.

24 likes 5d

o.nybergTL224 Jul 2026#77

Collapsed as off-topic by two members at trust level 3 or above

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.

ZieglerTL3Regular26 Jul 2026#78

footnote_entry, post #50: 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

1 like in reply to #50 2d

i.grimaldiTL2 Moderator27 Jul 2026#79

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.

1 like 19h

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Fasting versus non-fasting and which tests care posts 61–79

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