Detection of Dementia Cases in Two Swedish Health Registers: A Validation Study

Abstract

Background:Population-based health registers are potential assets in epidemiological research; however, the quality of case ascertainment is crucial.Objective:To compare the case ascertainment of dementia, from the National Patient Register (NPR) and the Cause of Death Register (CDR) with dementia diagnoses from six Swedish population based studies.Methods:Sensitivity, specificity, and positive predictive value (PPV) of dementia identification in NPR and CDR were estimated by individual record linkage with six Swedish population based studies (n = 19,035). Time to detection in NPR was estimated using data on dementia incidence from longitudinal studies with more than two decades of follow-up.Results:Barely half of the dementia cases were ever detected by NPR or CDR. Using data from longitudinal studies we estimated that a record with a dementia diagnosis appears in the NPR on average 5.5 years after first diagnosis. Although the ability of the registers to detect dementia cases was moderate, the ability to detect non-dementia cases was almost perfect (99%). When registers indicate that there is a dementia diagnosis, there are very few instances in which the clinicians determined the person was not demented. Indeed, PPVs were close to 90%. However, misclassification between dementia subtype diagnoses is quite common, especially in NPR.Conclusions:Although the overall sensitivity is low, the specificity and the positive predictive value are very high. This suggests that hospital and death registers can be used to identify dementia cases in the community, but at the cost of missing a large proportion of the cases.

Diagnosing type 2 myocardial infarction in clinical routine. A validation study

“…Hence, a high PPV may not be expected for a sub-diagnosis constituting a minority of the investigated population, as in the case of type 2 MI. Validation studies on sub-diagnoses tend to report low PPV:s, especially for rare sub-diagnoses, as has been shown for other conditions like dementia [14].…”

Lipid lowering and Alzheimer disease risk: A mendelian randomization study

“…Fourth, differences between the IGAP and PGC samples are also worth noting; in particular, a modest proportion of AD cases in the PGC sample were diagnosed from linkage to in‐ and outpatient health care records after the latest clinical assessments of these individuals were conducted (up to 741 cases, 27% of the PGC case sample). Individuals with other forms of dementia may have been misclassified as AD cases, or AD cases as controls, at higher rates with this type of ascertainment than in case–control or cohort studies with direct clinical assessments and/or pathological confirmation of AD . This could bias exposure–outcome association estimates if the exposures under study relate to the chance of misclassification differentially, for example, if an exposure increases the risk of hospitalization and, therefore, raises the likelihood of AD detection.…”

“…Individuals with other forms of dementia may have been misclassified as AD cases, or AD cases as controls, at higher rates with this type of ascertainment than in case-control or cohort studies with direct clinical assessments and/or pathological confirmation of AD. 50 This could bias exposure-outcome association estimates if the exposures under study relate to the chance of misclassification differentially, for example, if an exposure increases the risk of hospitalization and, therefore, raises the likelihood of AD detection. However, this would not be expected to explain an inverse association of a trait affecting CAD risk with lower AD risk, as we observe for PCSK9 variation.…”

Shift work and risk of incident dementia: a study of two population-based cohorts

“…Since only inpatient and outpatient care records were included in the NPR, dementia diagnoses performed only at the primary care level were undetected, though cases are mainly diagnosed in specialist care in Sweden [ 26 ]. However, previous validation work on Swedish register-based dementia diagnoses report moderate sensitivity of 63% and very high specificity of 99.8% [ 27 ]. Altogether, since misclassification of dementia is unlikely differential with respect to the exposure, i.e.…”