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July 3, 2000

Blood Tests and Insulin Injections

Question from Denver, Colorado, USA:

With all the questions about the differences between whole blood glucose values and plasma values, why is it so difficult to get a chart with normal plasma values? Whenever someone asks about the subject, they seem to be given a conversion formula and not a chart with a range like I've always had with whole blood readings.


Plasma glucose is about 15% higher than whole blood glucose. Labs have used plasma glucose for a long time: decades.

Meters used to use whole blood glucose; but now, every new meter introduced in the past 3-4 years is calibrated to plasma glucose. That way, the numbers are more like the lab. It’s not perfect though. Remember your meter costs only a few dollars, not thousands of dollars like lab instruments.

Why are there no charts: beats me! One might argue, just use the old chart; the blood glucose control will be better. Actually I do tell my patients about the low end of the spectrum, the 50s and 60s, and then let them be a bit lower in the high range.