There are no standards for lpstat behavior - mine simply reports an error. Yours seems to do interesting things, so let's investigate before we can answer your question.

Run your lpstat command from the prompt.
Next echo $?
Example
echo $? should produce a non-zero value (return code) on errors or warnings.
Is that what you see?

If that is the case, then you can use $? to have your code ignore any text output.