Combining blood tests and ultrasound scans are the best way to screen for ovarian cancer, British doctors say in a report that may not end the debate about how to catch the disease at its earliest and most treatable stages.

Ovarian cancer is sometimes referred to as "the silent killer," and only 45 per cent of patients survive five years. It is often detected only after it has spread throughout the abdomen, partly because its symptoms -- which include bloating and abdominal pain -- are so vague, most women are not diagnosed until it is too late.

Currently, there is no effective screening test to detect early stage disease. But the authors of this latest study say that with recent advances in transvaginal ultrasound and better interpretation methods for the CA125 tumour marker blood test, screening could now be possible.

In the study, doctors enrolled about 200,000 women aged 50 to 74 across the United Kingdom from 2001 to 2005.

About 100,000 of those women received no screening tests. The remaining half were split into two groups. Roughly 50,000 were screened with a blood test. If the blood test results suggested an abnormality, they then had an ultrasound. The rest of the women, nearly 50,000, received an ultrasound only.

In all, 58 cases of ovarian cancer were detected at first screening, and 48 per cent of them were in the early stages.

In the women who used both tests together, doctors caught 90 per cent of ovarian cancer cases. Using the blood test method, ovarian cancer was picked up 89 per cent of the time. With the ultrasound, the rate was about 75 per cent.

Nearly half the cases were in the stage I or stage II phases in which the cancer has not spread far and can sometimes be cured.

The study authors, Ian Jacobs and Usha Menon of University College London, report in the journal Lancet Oncology that they believe their findings are encouraging.

"We have now demonstrated we can pick up the vast majority of women with ovarian cancer earlier than they would have otherwise been detected and before they have symptoms," said Dr. Jacobs, "and that a good proportion of those women have earlier stage disease than we would normally expect them to have."

But the researchers warned there were problems. Many of the women in the trial had false positive results that led to unnecessary surgeries -- especially among those who had ultrasound scans alone.

What's more, it is not clear whether the tests reduced the death rate from ovarian cancer among the women in the study. Researchers must wait until the study finishes in 2014 to look at all the data.

"While preliminary, these encouraging data demonstrate that we may be able to use current affordable technologies to detect ovarian cancer at a curable stage," Dr. Beth Karlan, of the American Society of Clinical Oncology, said in a statement.

"Further follow-up should help us determine if these approaches can be cost-effective and truly reduce deaths from ovarian cancer."