Risk of an abnormal smear test does decrease with age
Cervical screening continues to pick up abnormalities in women over 50, say UK researchers, despite calls to cut the programme in older women.
There has been "much discussion" about whether to continue smear tests in 50 to 64 year olds, the Institute of Cancer Research team said.
But a study of two million women found serious cases would not be picked up if screening was removed in this group.
Around 2,700 women are diagnosed with cervical cancer each year in the UK.
The disease is the second most common cancer in women under 35 and in 99% of cases is caused by the common sexually transmitted infection HPV.
The idea behind screening is to pick up pre-cancerous changes and treat them before they become an invasive disease.
Women over 50 have a lower incidence of these changes or "lesions" with 10% of women in their 20s having abnormalities but only 1% in those over 50.
Previous studies have concluded that because the risk is lower in older women, screening may be causing more harm than good.
But a study of smear tests done in women aged 20 to 64 years between 1988 and 2003 found that screening does in fact pick up serious abnormalities, the British Journal of Cancer reported.
It showed two-thirds of abnormal smears were picked up in women who had two previous negative results in their 40s.
Removing screening in older women, even in those who have had no prior signs of lesions, would miss a group of women who develop abnormalities later in life, the researchers said.
The study was carried out in the south of England where the risk of cervical cancer is less than average and so even more cases might be missed in other areas of the country they said.
Currently, women aged 25 to 49 are invited for screening every three years, and 50 to 64 every five years in England.
The government is reviewing the age at which screening starts as women are invited for tests at age 20 in other UK countries.
Study leader Dr Roger Blanks said if you could stop screening at 50 that would save a huge amount of money and anxiety.
"But the data we have is there is not this dramatic decrease so we can't say they are no longer at risk."
He added further research was needed to see if there were any "very low risk groups" where screening could be stopped.
Dr Anne Szarewski, clinical consultant for Cancer Research UK, said that sexually transmitted infections are rising at a faster rate in people over 45 than in any other age group.
"We know that screening saves lives - this message has been loud and clear for younger women in recent months.
"This large study adds to the recent evidence that women over 50 should continue to be screened, as they continue to be at risk of developing cervical cancer."