This work extends previous investigations of the AD814,15
in two important ways. First, community-dwelling older adults with a low rate of dementia were sampled for this study, rather than relying on convenience samples of older adults with much higher base rates of dementia. Second, the study sample included only African Americans, an understudied group in dementia assessment research.
A key finding of this preliminary investigation was that an informant-based dementia screening tool was successfully applied in a sample of African Americans recruited from a large epidemiologic study. The AD8 averaged less than 3 minutes to complete. Informants were more likely to be friends of participants and less likely to be spouses in this community sample when compared to informants in clinic-based samples.14,15
Identification of an informant was not a major barrier to conducting this ancillary study to the AAH project; only 6% (14 / 252) of subjects contacted from the parent study were unable to identify an informant. The percentage without an informant in this study is slightly higher than that reported for clinic-based samples,15
yet is still low enough to permit an informant-based measure, such as the AD8, to be used in epidemiologic research. Nonetheless, the findings regarding informant availability in AAH are preliminary because only 54% (252 /465) of AAH participants to whom a recruitment letter was sent were contacted by telephone and the 32% (147 / 465) participation rate was low (in part, because funding constraints precluded a study sample above 150). It is plausible a higher percentage of AAH participants would not be able to identify a reliable informant to complete the AD8. Older individuals (e.g., ages 75+) might also be less likely to be able to identify reliable informants.
This study provides preliminary evidence that the AD8 is a useful tool for distinguishing between CDR 0 from CDR 0.5 in a population-based sample of an important disadvantaged minority group (African Americans). The distinction of CDR 0 from CDR 0.5 with the AD8 was supported by worse performance for the CDR 0.5 groups on an independent measure (the delayed recall WMS LM) of episodic memory, which is affected in early-stage dementia.33,34
The AD8 may be detecting cognitive problems at a stage before the degree of cognitive decline detected by tests such as the MMSE or SBT is evident and hence prior to the recognition of cognitive impairment that is based on cut-off scores on screening tests such as the MMSE or SBT.35
Informant-based measures, such as the AD8, identify memory and thinking problems through use of an individual as his/her own control, thereby avoiding know confounds or biases (e.g., education) of other dementia screening measures, such as the MMSE or SBT. In this preliminary study, the performance-based measures, MMSE and SBT, did not effectively discriminate between CDR 0 and CDR 0.5. Clinical impression ratings using the BIDD were better than the MMSE or SBT and overall achieved good discriminative ability for CDR 0.5. The AD8 alone was the most effective measure for discriminating between CDR 0 and CDR 0.5.
There are other limitations for this preliminary study. The AD8 is a screening tool, so follow-up assessments are needed to confirm the validity of the identified cognitive impairment as well as to complete the differential diagnosis of dementia. The study sample was small, the participation rate was low (32%), participants were relatively young for the occurrence of dementia, and individuals were only eligible for participation in the parent AAH study if their MMSE scores were 16 or higher; these factors may reduce external validity. The reliability of the AD8 has yet to be established among non-Caucasian samples. The CDR was selected as the gold standard based on its demonstrated sensitivity and accuracy in a research sample in which it has been shown to be a valid indicator of longitudinal progression to dementia severity 36,37
and by neuropathologic diagnosis of dementia.38,39
The degree to which CDR 0.5 is predictive of greater cognitive decline and dementia is uncertain in the current study sample without longitudinal follow-up investigations. There was a low frequency of diagnosed dementia at the CDR 0.5 stage, as might be expected given the mean age of the sample (61 y); more commonly, uncertain dementia was identified. Longitudinal follow-up also is required to validate that the BIDD is detecting cognitive impairment caused by dementia or other conditions (e.g., depression). The potentially greater sensitivity and specificity of the AD8 alone rather than combined with brief neuropsychological tests of the participant in the BIDD needs to be evaluated in a larger sample with more individuals with diagnosed dementia. Even with these limitations, however, the AD8 appears to have potential as a portable dementia screening instrument feasible to use in an African American community sample.
In summary, the AD8 is a brief, acceptable, easily-administered, informant-based dementia screening instrument that compares individuals against their prior cognitive function. In this preliminary study, the AD8 demonstrated high sensitivity and specificity for distinguishing CDR 0 from CDR 0.5 and, among a subset of AAH participants, informant availability was not a barrier to study participation; additional studies with larger samples, with higher participation rates, higher dementia rates, and older participants are warranted to confirm these findings. The AD8 may prove useful as a screening instrument for early dementia in clinical venues as well, especially once dementia-remittive therapies become available.