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Plasma-calibrated meters give higher readings than those which are whole blood calibrated. Laboratory equipment also references plasma, which is why people who use whole-blood-referenced meters at home often are surprised when their laboratory HbA1c readings come back higher than they expected. Now some are getting those higher plasma readings at home.
What does this mean for self-care for people with diabetes? Experts say the first step is to verify the calibrations of their meters.
Plasma readings are about 12 percent higher than whole-blood readings. For example, the same blood sample would read 140 on a whole-blood and 157 on a plasma-referenced meter.
The key is to use either type of meter consistently, says June Biermann, coauthor of nine books on diabetes and publisher of the newsletter, The Diabetic Reader. People with diabetes use different meters during the day, but this becomes dangerous if one references plasma and the other whole blood. The difference in numbers could lead to incorrect insulin doses.
Read the Fine Print
LifeScan's FastTake meter caused confusion during the autumn of 1998 because it references plasma but many people did not know. Many LifeScan customers were accustomed to receiving whole-blood numbers from a One Touch, and the plasma numbers threw them off.
Either type of meter can be up to 20 percent off and still meet FDA standards. The danger comes from taking too much or too little insulin.
Here's an example of the danger of using two differently referenced meters, exacerbated by a 20-percent variation. This is a worst-case scenario, but it brings out the importance of knowing your meter.
With a whole-blood meter, the glucose level is 140, but if the meter is 20 percent too low, the meter reads 112. With the same blood sample, on a plasma meter, the level is 157, but if the meter is 20 percent too high, the reading is 188.
With a 188 reading before a meal, many would need supplemental insulin; with the 112 reading, extra insulin would not be necessary. You could be in danger of getting the wrong dose.
Both the 188 and the 112 readings are accurate readings. Some see this wide range as frustrating for self-care, but, as one industry insider says, a $50 instrument cannot be expected to perform like $150,000 lab equipment.
Is this really a big deal? Yes, say most experts, but knowledge can prevent mistakes. Use this page to check the calibrations of your meters, to make sure that all your meters are similarly referenced.
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