09.07.14
Accuracy of blood test for Alzheimer’s may be overestimated
Research into developing a blood test to predict the onset of Alzheimer's disease has come under criticism with the results ‘no better than a coin test’.
In analysis on the NHS Choices website, Bazian, part of the Economist Intelligence Unit, noted that as there is no cure for Alzheimer’s, people may question whether an early warning system is of any practical use.
Additionally, it was claimed that the results of the research conducted by King’s College London, and co-funded by Alzheimer’s Research, which identified a set of proteins in the blood that can predict the start of the dementia with 87% accuracy, may have been overestimated.
The analysis on the NHS Choices website said: “An important point is that, while the test accuracy rate of 87% sounds impressive, it may be a large overestimate of what would happen in reality.
“This research developed and tested a new blood test that predicted the progression from mild cognitive impairment to Alzheimer’s disease, with an accuracy of 87% approximately a year before development.
“However, in a non-experimental setting, the test may be much less effective than the 87% figure suggests. Based on figures from the Alzheimer’s society indicating that 10-15% of people progress from mild cognitive impairment to Alzheimer’s disease each year, the test is only correct around 50% of the time – no better than a coin toss.
“However, the test is unlikely to be used by itself, so its predictive ability may be improved if used in combination with other tests in development. The predictive ability of the test would also improve if the 10-15% assumptions turned out to be an underestimate.”
“A further limitation is that it only made its predictions a year in advance of Alzheimer’s diagnosis. This is certainly better than nothing, but Alzheimer’s disease is often diagnosed at a later stage, with the disease having already caused damage for many years.”
As part of the research, published in the journal Alzheimer's & Dementia, scientists studied blood samples from 1,148 volunteers. Of the participants, 452 did not have dementia, 476 had Alzheimer’s and 220 had mild cognitive impairment (MCI). Mild cognitive impairment is a term used to describe early memory and thinking problems, which do not necessarily lead onto Alzheimer’s, but can put people at a higher risk of the disease.
The researchers analysed blood samples from the volunteers for 26 proteins previously linked to Alzheimer’s disease. They found that several of these proteins associated with brain shrinkage on brain scans in people with MCI and Alzheimer’s. Taking their research a step further, the team investigated whether any of the proteins could predict the progression from MCI to Alzheimer’s. They discovered a panel of 10 proteins that were able to predict which volunteers with MCI would go on to develop Alzheimer’s within a year.
Dr Abdul Hye, lead author of the study from the Institute of Psychiatry at King’s College London, said: “Memory problems are very common, but the challenge is identifying who is likely to develop dementia. There are thousands of proteins in the blood, and this study is the culmination of many years’ work identifying which ones are clinically relevant.
“We now have a set of 10 proteins that can predict whether someone with early symptoms of memory loss, or mild cognitive impairment, will develop Alzheimer’s disease within a year, with a high level of accuracy.”
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