Scientists have developed a blood test that can accurately diagnose or even predict Alzheimer's disease before symptoms appear, The Week says.

Currently the only way to definitively diagnose Alzheimer's disease in life is through brain scans and tests of cerebrospinal fluid that must be collected via lumbar puncture.

Though cumbersome and expensive, such tests provide the most accurate diagnoses for patients.

Researchers at the Brigham and Women's Hospital in the US are working to develop a blood test that could replace these procedures.

The tau protein has long been implicated in Alzheimer's, however, tau occurs as a family of related molecules which have subtly different properties.

The team took advantage of the complexity of tau and built assays to measure different forms of tau and identified a subset of tau proteins which are specifically elevated in Alzheimer's disease.