Study of Cardiovascular Health Outcomes in the Era of Claims Data: The Cardiovascular Health Study

Abstract

Background: Increasingly, the diagnostic codes from administrative claims data are being used as clinical outcomes.

Methods and results: Data from the Cardiovascular Health Study (CHS) were used to compare event rates and risk factor associations between adjudicated hospitalized cardiovascular events and claims-based methods of defining events. The outcomes of myocardial infarction (MI), stroke, and heart failure were defined in 3 ways: the CHS adjudicated event (CHS[adj]), selected International Classification of Diseases, Ninth Edition diagnostic codes only in the primary position for Medicare claims data from the Center for Medicare & Medicaid Services (CMS[1st]), and the same selected diagnostic codes in any position (CMS[any]). Conventional claims-based methods of defining events had high positive predictive values but low sensitivities. For instance, the positive predictive value of International Classification of Diseases, Ninth Edition code 410.x1 for a new acute MI in the first position was 90.6%, but this code identified only 53.8% of incident MIs. The observed event rates for CMS[1st] were low. For MI, the incidence was 14.9 events per 1000 person-years for CHS[adj] MI, 8.6 for CMS[1st] MI, and 12.2 for CMS[any] MI. In general, cardiovascular disease risk factor associations were similar across the 3 methods of defining events. Indeed, traditional cardiovascular disease risk factors were also associated with all first hospitalizations not resulting from an MI.

Conclusions: The use of diagnostic codes from claims data as clinical events, especially when restricted to primary diagnoses, leads to an underestimation of event rates. Additionally, claims-based events data represent a composite end point that includes the outcome of interest and selected (misclassified) nonevent hospitalizations.

Keywords: epidemiology; heart failure; incidence; myocardial infarction; stroke.

Figure 1

A. Incidence of MI per 1000 person-years by age categories for adjudicated CHS events, CMS events with ICD9 of 410 in first position or in any position, n = number of MI events, probable and definite, adjudicated within each age group. B. Incidence of stroke per 1000 person-years by age categories for adjudicated CHS events, CMS events with ICD9 of main stroke codes in first position or in any position, n = number of stroke events, probable and definite, adjudicated in each age group. C. Incidence of heart failure per 1000 person-years by age categories for adjudicated CHS events, CMS events with ICD9 of main HF codes in first position or in any position; n= number of HF events, probably and definite, adjudicated in each age group

Figure 1

A. Incidence of MI per 1000 person-years by age categories for adjudicated CHS events, CMS events with ICD9 of 410 in first position or in any position, n = number of MI events, probable and definite, adjudicated within each age group. B. Incidence of stroke per 1000 person-years by age categories for adjudicated CHS events, CMS events with ICD9 of main stroke codes in first position or in any position, n = number of stroke events, probable and definite, adjudicated in each age group. C. Incidence of heart failure per 1000 person-years by age categories for adjudicated CHS events, CMS events with ICD9 of main HF codes in first position or in any position; n= number of HF events, probably and definite, adjudicated in each age group

Figure 1

A. Incidence of MI per 1000 person-years by age categories for adjudicated CHS events, CMS events with ICD9 of 410 in first position or in any position, n = number of MI events, probable and definite, adjudicated within each age group. B. Incidence of stroke per 1000 person-years by age categories for adjudicated CHS events, CMS events with ICD9 of main stroke codes in first position or in any position, n = number of stroke events, probable and definite, adjudicated in each age group. C. Incidence of heart failure per 1000 person-years by age categories for adjudicated CHS events, CMS events with ICD9 of main HF codes in first position or in any position; n= number of HF events, probably and definite, adjudicated in each age group

Figure 2

A. Associations of incident MI with cardiovascular risk factors among 5,326 participants in the Cardiovascular Health Study (n for CHS[adj]=1006, n for CMS[1^st] = 605, n for CMS[any] = 847). Risk-factor estimates that were different from those for the adjudicated event estimate (reference) at the p<0.05 level with bootstrap methods are indicated with a [*] symbol. B. Associations of incident stroke with cardiovascular risk factors among 5,639 participants in the Cardiovascular Health Study (n for CHS[adj]=960, n for CMS[1^st] = 863, n for CMS[any] = 1248). Risk-factor estimates that were different from those for the adjudicated event estimate (reference) at the p<0.05 level with bootstrap methods are indicated with a [*] symbol. C. Associations of incident heart failure with cardiovascular risk factors among 5613 participants in the Cardiovascular Health Study (n for CHS[adj]=1759, n for CMS[1^st] = 544, n for CMS[any] = 1919). Risk-factor estimates that were different from those for the adjudicated event estimate (reference) at the p<0.05 level with bootstrap methods are indicated with a [*] symbol.

Figure 2

A. Associations of incident MI with cardiovascular risk factors among 5,326 participants in the Cardiovascular Health Study (n for CHS[adj]=1006, n for CMS[1^st] = 605, n for CMS[any] = 847). Risk-factor estimates that were different from those for the adjudicated event estimate (reference) at the p<0.05 level with bootstrap methods are indicated with a [*] symbol. B. Associations of incident stroke with cardiovascular risk factors among 5,639 participants in the Cardiovascular Health Study (n for CHS[adj]=960, n for CMS[1^st] = 863, n for CMS[any] = 1248). Risk-factor estimates that were different from those for the adjudicated event estimate (reference) at the p<0.05 level with bootstrap methods are indicated with a [*] symbol. C. Associations of incident heart failure with cardiovascular risk factors among 5613 participants in the Cardiovascular Health Study (n for CHS[adj]=1759, n for CMS[1^st] = 544, n for CMS[any] = 1919). Risk-factor estimates that were different from those for the adjudicated event estimate (reference) at the p<0.05 level with bootstrap methods are indicated with a [*] symbol.

Figure 2

A. Associations of incident MI with cardiovascular risk factors among 5,326 participants in the Cardiovascular Health Study (n for CHS[adj]=1006, n for CMS[1^st] = 605, n for CMS[any] = 847). Risk-factor estimates that were different from those for the adjudicated event estimate (reference) at the p<0.05 level with bootstrap methods are indicated with a [*] symbol. B. Associations of incident stroke with cardiovascular risk factors among 5,639 participants in the Cardiovascular Health Study (n for CHS[adj]=960, n for CMS[1^st] = 863, n for CMS[any] = 1248). Risk-factor estimates that were different from those for the adjudicated event estimate (reference) at the p<0.05 level with bootstrap methods are indicated with a [*] symbol. C. Associations of incident heart failure with cardiovascular risk factors among 5613 participants in the Cardiovascular Health Study (n for CHS[adj]=1759, n for CMS[1^st] = 544, n for CMS[any] = 1919). Risk-factor estimates that were different from those for the adjudicated event estimate (reference) at the p<0.05 level with bootstrap methods are indicated with a [*] symbol.

Figure 3

Risk factor associations for incident adjudicated MI (n=1006 events) and the same risk-factor associations for all first hospitalizations (n=4981 events) not due to an MI among 5,326 CHS participants free of baseline MI events. Risk-factor estimates that differed between adjudicated incident MI and the first non-MI hospitalization at the p<0.05 level with bootstrap methods are indicated with a [*] symbol.