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SerialStateLineXer t1_j4vcgpv wrote

Reply to comment by sometimesgoodadvice in 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? by rsbanham

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.

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