In most cases, we don’t really care if the numbers we see are exactly the same as the lab. What we care about is how they change with different foods and what our particular meter says when we feel low.
So if you feel low at 65 with one meter and 75 with another, that’s what you should remember.
There are two factors involved here: Accuracy and precision. Accuracy means how close to lab values your meter is. Precision means how repeatable the measurements are.
So if lab value is 80 and your meter reads 79, 81, 80, your meter is both accurate and precise.
If your meter reads 89, 90, 89, your meter is precise but inaccurate.
If your meter reads 75, 82, 85 (average is 80), your meter is accurate but imprecise.
I was once told by a company tech support person, that smaller drops of blood are more strongly affected by a lttle interstitial fluid, and the amount of interstitial fluid depends on whether or not you milk the finger. After you’ve eaten, blood and interstitial fluid levels vary more than when fasting.
And even lab values aren’t always accurate. If blood sits around, the glucose levels decrease, and I once discovered that the office where I gave blood let it sit around for almost 7 hours before sending it over to the hospital lab. I stopped giving blood there.
Furthermore, labs are run by humans, and humans sometimes make mistakes. When I worked in a research lab, we always measured everything in triplicate to try to control for small procedural errors or dirty test tubes or whatever.
So I think our best bet is to assume our BG readings are pretty good approximations, but we shouldn’t panic if something changes a reading 5 points. It’s meaningless. If one reading seems wrong, then test again. The important thing is consistency, using the same meter the same way every time.