The 21-question test distinguishes between normal forgetfulness and the more worrying memory lapses that could signal the early stages of dementia.

Doctors who have developed the test say it is almost 90 per cent accurate. Designed to be answered by a spouse or close friend it measures mild cognitive impairment - the slight memory lapses that can be a precursor of the disease.

It is thought that around 15 per cent of people who are diagnosed with mild cognitive impairment go on to develop Alzheimer's within a year. It was devised by Banner Sun Health Research Institute in Arizona, which specializes in the disease.