How do blood labs determine what is “normal”? Do they use average Americans who are obese and have diabetes and high blood pressure etc, or do they use “healthy” people?

Question

For example: Normal isn’t the same as optimal. Smoking used to be normal.

So if it says normal Vitamin D levels are 60 does that mean it’s the optimal level or just what level is common?

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Answer 1

When they say “normal” it’s the level where they don’t see adverse effects, not just the median of all people 🙂

Answer 2

Test results that use terms like “normal” are reflecting values that are “within range” – meaning an acceptable range for optimal health. Anywhere within range is “fine”, though teetering on the edge of something doesn’t necessarily mean you’re going to suddenly drop dead. These determinations are made based on all the current data at a given time regarding optimal health, and therefore subject to change somewhat over time as science informs us. For example, blood pressure ranges were re-identified not so long ago to make anything over 120 systolic concerning on its own, whereas it used to not be a big deal if it were up to 130, as long as diastolic was under 80. Cholesterol types and ranges have also been modified. These numbers are not based on unhealthy population data however, but rather, what’s considered ideal for good health.

Edited to delete extra garbage and clarify.

Answer 3

Normal in this context is just meaning “within healthy ranges”

So values falling outside of healthy ranges would suggest the presence of disease, injury or other irregularity

Sometimes, having a higher than normal or lower than normal result may actually be expected too and would be noted.
For example a lot of people will have a decreased vitamin d level in areas where the sun is only up for a few hours during winter, this would be “normal” for the population but it would not be seen as “normal” in regards to a blood test because it is outside healthy ranges. Luckily it’s easily fixed by supplanting and/or using lamps