Researchers say the breakthrough will now make it easier to track and treat the condition.

Further tests could then be used to determine the severity of a patients' condition and course of treatment.

Scientists from the University of Pennsylvania School of Medicine discovered that the urine test could detect damage associated with mild cognitive impairment (MCI), such as memory loss, which is recognised as a precursor to Alzheimer's.

It is widely believed that accurate early diagnosis of Alzheimer's is vital if we are to offer an effective long-term treatment for this devastating disease

Rebecca Wood of the Alzheimer's Research Trust

Test results

The test detects isoprostanes, chemicals which scientists believe are released in the brain as a result of Alzheimer's damage.

Within four years of being diagnosed with MCI, up to half the sufferers will go on to develop Alzheimer's.

Domenico Pratico, assistant professor in Penn's Department of Pharmacology, said the test could help doctors slow the progress of the disease if they catch it early enough.

"This is the first non-invasive test that can predict a clinical diagnosis of Alzheimer's disease.

"Since there is no cure for Alzheimer's disease, physicians could slow the course of the disease if it is caught early enough."

In their study, published in the Archives of Neurology, Professor Pratico and his team studied 123 people, 50 of whom had Alzheimer's and 33 who had MCI.

The new test is not widely available at the moment, but the team is developing a more user friendly version.

Hope

Rebecca Wood, chief executive of the Alzheimer's Research Trust said a test like this would offer hope to sufferers.

"It is widely believed that accurate early diagnosis of Alzheimer's is vital if we are to offer an effective long-term treatment for this devastating disease.

"There is a lot of work taking place to find an accurate, cheap, and non-invasive way of diagnosing Alzheimer's early, including a major project in London being funded by the Alzheimer's Research Trust.

"These results from the US could be promising, but it will be necessary to do significant further research to expand on this work."