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November 23, 2003

Blood Tests and Insulin Injections

Question from Antelope, California, USA:

Recently, my 12 year old son, who has type�1 diabetes, had a rather large drop of blood and wanted to quickly retest the same drop of blood using a second test strip. The second test, using the same drop of blood, within 60 seconds of the first test, read much higher than the first test. He has now tried this experiment several times, always with the same result. The second reading is substantially higher (20-30 mg/dl [1.1-1.6 mmol/L]). We have "tested" our meter and called our diabetes coordinator, but we are not satisfied with her explanation. If the same drop of blood gives different results, can we trust our meter?


Some of the old meters do indeed have quite a lot of variation between sample readings, but this would not explain the recent consistently higher second reading. In working this all out, I think that the first step would be to repeat this sampling once more, but in addition to calibrate the meter right before and after the sample assays, and the next would be for you to do the same on yourself at some time when your son was not present. If these steps consistently confirm your son’s observations and the meter is not a new one then you may have a case to seek a replacement. In the long run it might be best to try Alternate Site Testing using one of the new meters like the FreeStyle Flash which uses a very small forearm sample and are essentially painless.

Additional comments from Stephanie Schwartz, diabetes nurse specialist:

This would be a problem only if the blood sugar in the lower ranges. Meters can vary by 10-15% so if the first reading was 100 mg/dl [5.6 mmol/L], and the second was 130 mg/dl [7.2 mmol/L], this might be of some concern. However, if the reading was 200 mg/dl [11.1 mmol/L] and then 230 mg/dl [12.8 mmol/L], it would be within the tolerance of the meter.

If control solutions give accurate results, I would not be concerned. To ease you mind, you might want to also check the meter against a value run in a laboratory. The bottom line is would that difference have made any difference in what you did?