Original article
The accuracy of medicare claims data in identifying Alzheimer's disease

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Abstract

We linked Medicare claims data to information on 417 patients with a clinical diagnosis of Alzheimer's disease in the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) to determine what proportion of them were identified as having Alzheimer's disease (AD) in Medicare claims records. Seventy-nine percent of these patients were identified as having AD using 5 years of claims data; 87% were identified as demented when a broader set of ICD-9-CM codes was used. An Anderson-Gill counting process approach was used to model the “hazard” of patients being identified as having AD in Medicare claims data. CERAD patients with mild dementia were less likely to be identified in the claims data as having AD. Once identified in Medicare claims as having AD, patients were more likely to be so identified again. When using only the physician supplier and institutional outpatient files, approximately 75% of CERAD patients were identified as having AD; hospital files used alone identified less than one-third (29%) of the CERAD patients as having AD. The data indicate that at least 3 consecutive years of physician supplier and physician outpatient claim files should be used to identify Medicare beneficiaries with AD using Medicare claims.

Introduction

Medicare claims records allow for the study of cost and outcomes in broadly representative samples of persons, but it is not known how reliable ICD-9-CM diagnosis codes contained in claims data are for identifying persons with Alzheimer's disease (AD). Several publications using Medicare claims records to identify prevalent cases of the disease appear to have seriously underestimated the prevalence of AD when compared with the estimated prevalence in the elderly population as a whole 1, 2, 3, 4, 5. Such undercounting may bias the results of work based on a Medicare claims-based estimate of prevalent cases of AD. This raises the issue of how reliable Medicare claims data are in identifying AD, whether the apparent undercount of prevalent AD is systematic, and if so, what types of persons with AD are most likely to be missed. If the undercount of AD cases is systematic, it can be modeled and perhaps adjusted for in studies that rely on Medicare claims to identify prevalent AD.

The present study attempts to determine the accuracy of Medicare claims data in identifying AD in a population of persons 65 years of age and over, all of whom have a clinical diagnosis of AD. Our goal is to provide practical guidance to those who wish to use Medicare claims to identify cases of AD. To do so, we examined 5 years of Medicare claims data (1991–1995) for 417 patients with AD who participated in the Consortium to Establish a Registry for Alzheimer's Disease (CERAD).

Section snippets

Subjects

Subjects were drawn from the AD patients entered into CERAD. CERAD, funded by the National Institute on Aging, is a consortium of the memory disorders clinics at 23 major tertiary care medical centers, including all the Alzheimer's Disease Centers [6]. Eligibility criteria for entry into CERAD included age 50 or greater, mild to moderate AD with no other disorders that could affect the dementing condition, independently mobile, a score of greater than 0 on at least two of the five

Descriptive results

Table 1 presents the number of AD and ADRD claims for the 417 patients examined. Roughly eighty (78.9%) percent had at least one Medicare claim during the study period that listed ICD-9-CM code 331.0 (Alzheimer's disease) as a diagnosis code. When using a broader definition of dementia that included additional ICD-9-CM codes, just under 90% (87%) of all persons had at least one Medicare claim with a diagnosis code signifying dementia. Many subjects had multiple Medicare claims that carried

Discussion

There was an undercount of patients with AD in our study. Our results, however, provide some support for using Medicare claims records to identify persons with AD, when Medicare claims allow examination of important research topics that could not otherwise be addressed.

When 3 years of Medicare claims data were used, approximately 75% of CERAD cases who were known to have AD were identified as having AD in Medicare claims; the identification rate rose to over 80% when we used a broader set of

Acknowledgements

This work was supported by NIH Grants No. AG06790, AG08937, and 1PO1-AG-17937. The authors thank Bercedis Peterson for help in data management and comments on the manuscript, and Albert Heyman and Carl Pieper for comments on the manuscript.

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