Lifescan ONETOUCH ULTRA2 Owner's Booklet page 38

If you continue to get unexpected results, check your system with control
solution. See control solution testing, pages 44–49.
If you are experiencing symptoms that are not consistent with your blood
glucose results and you have followed all instructions in this booklet, call
your healthcare professional. Never ignore symptoms or make significant
changes to your diabetes control program without speaking to your
healthcare professional.
A hematocrit (percentage of your blood that is red blood cells) that is
either very high (above 55%) or very low (below 30%) can cause false
results.
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CAUTION: Repeated unexpected glucose results
CAUTION: Unusual red blood cell count