Without more information, I can only assume the reason for denial. Please be more specific as to what you are billing out and what the Medicare denial is. G0438 and Q0091 can be billed together and no modifier is needed. What diagnosis is being submitted with the Q0091? Even if you have it listed as a dx but it is not pointed to the pap, it will deny. If it isn't one of the listed diagnoses, it will deny not medically necessary.