I have just been told that A, tests markers for blood tests and health checks etc (I dunno… testosterone, cholesterol, red blood cells) in the population are changing over time, and that B, the acceptable levels for such markers are changing with them. Is this true?

Submitted by rsbanham t3_10eo8kg in askscience

For example - in 1930 testosterone normal level in the population is 10 units . So when you have a blood test the normal range is 8-12.

In 2020 the normal level is 4 units, so the normal range has been adjusted to 2-6

I hope I am making sense, and I really hope to get an answer. To me this makes no sense. For sure adjustments are made based on better science, but not because the population is becoming unhealthier?

5

Comments

You must log in or register to comment.

sometimesgoodadvice t1_j4u9hi1 wrote

Really not sure about the premise and how much normal ranges actually change. Let's make an assumption that it is true thought and use some logic. What defines a normal range for a given biomarker? Let's say I was a really good scientist and wanted to do "better science" to find out what a healthy range for red blood cell count was. I would probably take a cross-section of people that doctors have called "healthy" and ones that they have diagnosed with a disease that affects RBC. Then I would do some nice statistics and say that 95% of people with with disease corresponding to low RBC had counts <3e12L and 95% of people with disease that correspond to elevated RBC had counts of >7e12/L. So I will define my "healthy" range as 3-7e12/L show that that corresponds to 98% of "healthy" people. Then I do some more statistics to determine false positive and negative rates, teach doctors how and when to properly utilize this knowledge (including performing the test exactly as I had) and be done.

There really is not a different way to do this. There is no equation that can tell you how many RB cells you need to have. There are some limits of upper and lower bounds, but those are not very useful, so we have to be empirical.

Now let's say I do this again, 50 years later and find that the value shifted. Is there a big problem? After all, the healthy range still corresponds to people that are "healthy" and the unhealthy range to those that have some underlying condition that doctors can diagnose. Maybe the range shifted because people in general have become "unhealthy". But then they would be diagnosed as such. It's just as likely that the range shifted because fewer people are eating lead paint, or because we decided to include people from diverse backgrounds with different genetics or environmental stimuli that were not available in the first study. Maybe the range shifted because people are much "healthier" now with more monitoring and resources available to stay healthy. As long as the range serves its purpose - identifying values that are indicative of an underlying disease - it does not matter what the absolute value is.

5

SerialStateLineXer t1_j4vcgpv wrote

One example of standards being revised due to people becoming healthier is blood lead levels. Back in the 60s, the US CDC used a threshold of 60 mcg/dL for high blood lead levels in children. Over time, as average blood lead levels come down, the threshold has been repeatedly revised downward, most recently to 3.5 mcg/dL.

Part of the reason for this, I suspect, is that back in the 60s they didn't have evidence that 3 mcg/dL was better than 5 mcg/dL because lead was so ubiquitous that they couldn't find a sample of children with levels low enough to test this hypothesis. They could tell that 80 was worse than 50, but the possibility that 3 might be better than 5 was purely hypothetical.

5

Alittlebitmorbid t1_j4varmd wrote

I think this has to do with several factors. I will use cholesterol as an example.

Factor A: testing methods change over time, I doubt the methods of 1930 were the same or as exact as they are today

Factor B: research of acceptable factors, cholesterol for example is usually divided into two sorts, and for years it was state of the art too high cholesterol of any sort is bad, then it changed to one sort being the "good" cholesterol, so higher levels should be tolerated of this kind and lower of the other kind

Factor C: this may surprise, but... pharma industry, they profit from lower tolerance as there is a huuuuge market for statins (I could name half a dozen statins right now), so they commission studies which show the wanted results and many people do not know how to look at the studies and results properly

Factor D: actual change in eating habits, genes, environment, etc.

3

ScienceIsSexy420 t1_j4w5jm3 wrote

You're point about testing methods is a great one, and I was going to make that point myself. I work as a chemist refining the next generation of testing methods, and when we use a new method we need to do large numbers of cohort studies, to document the normal ranges with the new methodology. A new methodology may make the averages go down, and it doesn't mean that everyone magically got healthier, it just means this new test is different.

I do have to be my naturally pedantic self and point out that there are not two kind of cholesterol. What you are referring to are actually called lipoproteins, for the life of my I don't know why we call them cholesterol but it's of course not just you. Cholesterol levels are an entirely different test, and there is only a single kind of cholesterol, called cholesterol. Lipoproteins are responsible for collecting, depositing, and moving around all of your lipids (triacylglycerides and cholesterol) throughout your body. HDL lipoprotein tend to play a role in the deposition of fats, especially arterial cholesterol, (which is why we call them "bad") while LDL lipoproteins tend to help to remove such deposits (why they are the "good" cholesterol). Importantly though, neither is actually a kind of cholesterol, of which there is only one (okay one natural cholesterol, I actually used to work in a synthesis lab where we specialized in making unusual forms of cholesterol).

1

Alittlebitmorbid t1_j4x8tzt wrote

Thank you for clarifying that, I did not know (and I'm a nurse)!

2

ScienceIsSexy420 t1_j4xzdyz wrote

My pleasure! As an added bonus that you didn't ask for at all, did you know that consumption of dietary cholesterol, and elevated endogenous cholesterol levels, are not well correlated? We don't really know what causes elevated cholesterol levels, but there's not much evidence that suggests that diet is a large contributing factor. Conversely, consumption of excess lipids can cause hyperlipidea.

Also, I labeled the good and bad cholesterol incorrectly in my previous comment, but I fixed it now. LDL=bad, HDL=good

1