Preventative, not diagnostic
It is important to note that smear tests are used to help prevent cervical cancer, rather than diagnose it. Cervical cancer does not develop suddenly, out of the blue, but cervical cells will change progressively over time.
This is why regular cervical screenings, at least once every three years, are highly recommended for all women between the ages of 25-49. Women between the ages of 50-64 should get screened at least once every five years.
Tests are designed to identify the smallest mutation. These will typically be categorised as pre-cancerous, before any serious complications arise in the cervix. This preventative approach to screening means that 1 in 20 women will receive an abnormal smear test result from their GP or private gynaecologist.