How effective is the Pap smear?

How effective is the Pap smear?
Regular Pap smears every two years can help prevent up to 90 per cent of the most common type of cervical cancer.

Like all screening procedures, the Pap smear has limitations. Sometimes it will not detect early cell changes because the smear did not contain enough abnormal cells. Sometimes samples are difficult to interpret due to blood or mucus on the slide. If this occurs, the general practitioner or nurse may need to take another Pap smear.