Clinical investigations
Accuracy of medicare claims-based diagnosis of acute myocardial infarction: estimating positive predictive value on the basis of review of hospital records

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Abstract

Background

Many cardiovascular epidemiologic studies rely on diagnosis codes in health care claims databases. Despite important changes in the care and diagnosis of acute myocardial infarction (AMI), the validity of hospital discharge diagnosis codes for AMI in the US Medicare system has not been recently examined. Our objective was to examine the accuracy of International Classification of Diseases—ninth revision—Clinical Modifications (ICD-9-CM) discharge diagnosis codes and diagnosis-related groups (DRG) codes for AMI in a Medicare claims database.

Methods

We sampled hospitalization episodes from Medicare beneficiaries in Pennsylvania during 1999, 2000, or both. We used Medicare data to identify patients with hospitalizations containing indicators of AMI (ICD-9-CM diagnosis codes 410.X0 and 410.X1 or DRG codes 121, 122, and 123). Hospital records for these episodes were reviewed by trained abstractors using World Health Organization criteria for diagnosing AMI. We then calculated the positive predictive value of Medicare claims-based definitions of AMI.

Results

Of 2200 hospitalization episodes with Medicare diagnosis codes suggestive of AMI, 2022 hospital records (91.9%) were obtained. The positive predictive value for a primary Medicare claims-based definition was 94.1% (95% CI, 93.0%–95.2%). Positive predictive values for alternative claims-based definitions ranged slightly, with the definition including DRG codes and length-of-stay restrictions yielding the highest positive predictive value, 95.4% (95% CI, 94.3%–96.4%). Subjects with a history of myocardial infarction had a significantly lower positive predictive value than subjects without a history of myocardial infarction (88.1% vs 94.6%, P <.001).

Conclusions

In this study, we observed high positive predictive values for a Medicare claims-based diagnosis of AMI and a diagnosis based on structured hospital record review.

Section snippets

Study population

Medicare beneficiaries in Pennsylvania who were also enrolled in that state's Pharmaceutical Assistance Contract for the Elderly in 1999, 2000, or both formed the available source population. The Pharmaceutical Assistance Contract for the Elderly is a state-run pharmacy benefits program that pays for medications for low-income elderly residents (annual gross income ≤$14,000 if single or $17,200 if married). The target population for this study were all hospitalization episodes during 1999 or

Results

Of the 2200 records for hospital episodes requested, 2022 (91.9%) were retrieved and reviewed. Of the 2022 reviewed, 1874 hospitalization episodes met the primary claims-based definition of AMI aforementioned. We excluded 23 hospitalization episodes that had missing data for >2 of 3 reference standard criteria, leaving 1851 hospitalization episodes in the final study sample.

Baseline characteristics of subjects included in the sample of hospital records (n = 2022) and subjects whose hospital

Discussion

We examined the positive predictive value of discharge diagnosis codes for AMI in a sample of Medicare beneficiaries from Pennsylvania. The positive predictive value for the primary claims-based definition we tested was 94.1%. All alternative claims-based definitions tested had similarly high positive predictive values when tested in the population overall. Secondary analyses found that the positive predictive value was lower among subjects with a history of MI in the year before the index

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Supported by a research grant from Merck. Dr Solomon also receives grant support from National Institutes of Health (grants K23-AR48616 and R55-AR48264). Dr Cannuscio is an employee of Merck.

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