According to a new study, those who have slight issues with these tests are more likely to develop mild cognitive impairment, which can be a precursor to dementia.

Some persons who report memory and cognitive problems show no evidence of a problem on standard testing, while others exhibit slight decreases. The study is published in Neurology.

"Several studies have found that people with subjective cognitive decline have an increased risk of dementia," said study author Michael Wagner, PhD, of the German Center for Neurodegenerative Diseases in Bonn.

"Our results now suggest that people with subjective cognitive decline who also have minor test deficits, or early signs of memory and thinking problems not yet reaching the diagnosis of mild cognitive impairment, may be more likely to progress to memory disorders. Testing for these deficits in people with self-reported decline could help identify people at a higher risk for progressing to mild cognitive impairment."

The study involved 439 people with subjective cognitive decline with an average age of 71 who did not have dementia or mild cognitive impairment.

Participants completed a series of tests to assess thinking and memory skills. Tests included memorising lists, copying a drawing, and correctly identifying time frames and current locations. Minor test deficits were defined as having a score of at least 0.5 standard deviations below the average score.

Mild cognitive impairment was diagnosed by a panel of researchers who reviewed each participant's performance across several tests. A test score of at least 1.5 standard deviations below the average was necessary for a diagnosis of mild cognitive impairment.

Of those with subjective cognitive decline, 13 per cent, or 55 people, had minor test deficits at the start of the study and 87 per cent, or 384 people, did not have minor deficits. Then the participants were followed for an average of three years to see who developed mild cognitive impairment.

After adjusting for age and sex, researchers found that people with subjective cognitive decline who also had minor test deficits were more than four times more likely to progress to mild cognitive impairment compared to people without minor deficits.

Researchers found that among the people with subjective cognitive decline, 17 per cent, or 58 people, who did not have minor deficits, and 48 per cent, or 24 people, who did have minor deficits, progressed to mild cognitive impairment.

Researchers also found that people with subjective cognitive decline and minor test deficits had a 36 per cent probability of developing mild cognitive impairment within two years and an estimated probability of 84 per cent of developing mild cognitive impairment within four years.

They also found that people with subjective cognitive decline and minor test deficits had higher levels of biomarkers measuring protein changes in the brain, indicating an increased risk of Alzheimer's disease.

"Our results shed new light on the link between subjective and objective decline before being diagnosed with Alzheimer's dementia," said Wagner. "Future research may help doctors to measure and communicate individual risk for people with subjective cognitive decline."