High False-Negative Rate in Cognitive Screening

by U.S. Medicine

July 5, 2016

SAN DIEGO—Existing screening tools for mild cognitive impairment (MCI) miss too many confirming diagnoses, according to a new study.

An article published in the Journal of Alzheimer’s Disease reports a false-negative error rate of 7%. Researchers at University of California San Diego School of Medicine and VA San Diego Healthcare System said that means that patients are misclassified as not having the condition based on standard screening instruments but actually do have MCI when more-extensive testing is conducted.1

“There are consequences to misdiagnosis,” said first author Emily C. Edmonds, PhD. “At the individual level, people incorrectly identified as cognitively normal might not receive appropriate medical advice or treatment. This could include preventive measures, such as diet or lifestyle changes to maintain cognitive function, or a referral to other healthcare providers.”

Furthermore, Edmonds said, diagnostic errors can negatively affect research studies of MCI and early Alzheimer’s disease, adding, “If research participants are misclassified when they enroll in a study, this can weaken the study’s results, which makes it even more difficult to find and develop effective treatments or therapies.”

Current diagnostic criteria for MCI rely upon subjective memory complaints by the person being screened, a single test score indicating impaired memory and clinical judgment.

“We have previously found that as many as one-third of MCI cases diagnosed with the standard method are false-positive errors,” Edmonds noted. “This, coupled with our recent finding of a 7 percent false-negative error rate, is concerning and tells us that the diagnostic criteria could be improved”

For the study, researchers examined data from 520 individuals participating in the Alzheimer’s Disease Neuroimaging Initiative, a nationwide, multi-institution study of MCI and Alzheimer’s disease. All of the participants, about half men and women with a mean age of 74.3 years, underwent standard MCI screening and a more in-depth diagnostic process that involved additional memory and learning tests.

Another 37, 7.1%, were identified as cognitively normal based on standard criteria but qualified for MCI diagnosis using the more-comprehensive testing. In addition to mildly impaired cognitive performance, they had biomarkers in their cerebrospinal fluid indicating risk for future dementia. The remaining participants tested normal using both methods—a true-negative rate of 92.9%.

The use of rigorous diagnostic criteria that include formal neuropsychological tests and less reliance on standard screening methods for MCI can improve clinical research studies and better predict who is likely to progress from MCI to dementia, study authors said, adding “The impact of ‘missed’ cases of MCI has direct relevance to clinical practice, research studies, and clinical trials of prodromal Alzheimer’s disease.”

1 Edmonds EC, Delano-Wood L, Jak AJ, Galasko DR, et al. Alzheimer’s Disease Neuroimaging Initiative. “Missed” Mild Cognitive Impairment: High False-Negative Error Rate Based on Conventional Diagnostic Criteria. J Alzheimers Dis. 2016 Mar 31;52(2):685-91. doi: 10.3233/JAD-150986. PubMed PMID: 27031477; PubMed Central PMCID: PMC4879874.

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