It’s natural to assume medical tests are valid and precise. But in reality, few meet these criteria.

Even if the test is accurate, mistakes can arise in the way it was executed, in calibration of equipment, specimen handling, and so forth.

This can lead to failure to see a health problem, or, on the other hand, a diagnosis of a disease that isn’t present. Those are false negatives and false positives, respectively. Serious consequences can and do follow from such errors.

Imagine taking a test for your cognitive health. The results show you do or don’t have dementia. Should you accept the findings? Let’s take a look. . .

The Three Quick Tests

Researchers from the University of Exeter, England, analyzed data on 824 older Americans with an average age of 82. They were evaluated for up to four hours by a clinical research nurse and a neuropsychology technician.

They were given a physical examination, an extensive neurological assessment, and checked for the Alzheimer’s-related APOE gene.

From all data and information gathered, an expert panel provided a diagnosis for each person. Just over one in three (35%) were judged as having dementia.

Once they had all the data, the participants undertook three quick tests commonly used in US primary care settings to assess cognition. These are the Mini-Mental State Examination (MMSE), the Memory Impairment Screen (MIS) and the Animal Naming (AN) test.

The MMSE assesses simple word, visual and time/space orientation capabilities. MIS asks subjects to recall four words they saw several minutes earlier. For the AN test, as many animals as possible must be named in 60 seconds.

If a family member or friend were present, they provided information about medications the patient was taking, family history, lifestyle, and their impression of the person’s cognitive abilities.

Inaccurate, Biased Results

The panel found 35.7% of cases (301 people), were misclassified by one of the tests. 13.4% were misclassified by two tests and 1.7% for all three.

The dementia misclassification rate for MMSE was the highest at 21%, followed by MIS at 16% and AN at 14%.

For the MMSE, years in education stood out, giving a false negative rate of 23%. The more educated a person, the more likely he or she was to do well on the test, even though, in reality, they had dementia.

Living in a nursing home gave a staggering 4.8-fold false positive in the AN test. Residents would be considered demented even though they were not.

For all tests, not having a friend or family member chip in with their own assessment increased the chances for misclassification. Older age and ethnicity also skewed the results.

One of the report’s authors, David Llewellyn, said, “Our study found that all three tests often give incorrect results that may wrongly conclude that a person does or does not have dementia.

“Each test has a different pattern of biases, so people are more likely to be misclassified by one test than another depending on factors such as their age, education and ethnicity.”

My comment is that it looks like there is some protection in taking all three, since very few people were misclassified by all three tests. But I doubt if it’s common practice to examine potential dementia patients so thoroughly.

What seems fairly clear is that no one should accept a dementia diagnosis based on one test. Nor, for that matter, a thumbs-up, all-clear signal based on one test.

Brief Tests are Imperfect

Lead author Janice Ranson added that “while these results are at first concerning, knowing the specific limitations for each test will help clinicians decide which is the most appropriate for their patient.”

Keith Fargo, PhD, director of scientific programs and outreach for the Alzheimer’s Association in Chicago, commented on the study by saying, “…all brief assessment tools for cognitive impairment are imperfect. That said, they are important to determine who needs more thorough evaluation to make an accurate diagnosis.”

Sending cognitively healthy people for detailed evaluation after false test results is troubling enough, but at least the additional testing should clarify their true state.

The greater concern is for those sent away with a clean bill of mental health after a brief test when they may be suffering with early dementia. Such people, and their loved ones, will be unaware that urgent diet and lifestyle changes are needed.


  1. http://cp.neurology.org/content/early/2018/11/28/CPJ.0000000000000566
  2. https://www.medpagetoday.com/neurology/dementia/76629

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