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August 25, 2000

Blood Tests and Insulin Injections

Question from Reisterstown, Maryland, USA:

We have a seven year old grandson who has had diabetes since the age of 18 months. Within the last two weeks, we have switched his glucose monitor from Meter "W" to meter "P". We understand that meter "P" reads the blood plasma and not the whole blood as does meter "W" and is closer to lab readings. We have also noticed dramatic changes in the readings (much, much lower), 25-35 mg/dl [1.4-1.9 mmol/L], and he's showing no signs of being low. Could this be the machine or because it's reading the plasma vs. whole blood? We have taken readings from both machines and on meter "W" he may be 57 mg/dl [3.2 mmol/L] and on meter "P" 35 mg/dl [1.9 mmol/L]. We're having trouble making insulin adjustments because of the drastic number changes in glucose readings. Any suggestions?

Answer:

There are meters with this sort of problem, with individual meters sometimes reading too high as well as too low. It is acceptable for plasma [also called serum] levels to be 6% lower than whole blood, but 40% low is much too large a difference. My advice to this family would be to return their meter until these difficulties are solved.

DOB