Ethnic, racial, and geographic differences influence virtually all human disease, and certain conditions exhibit well-established differences between Africans and Europeans.1  Once such differences are identified, it is important to examine them, because etiologic, genetic, and therapeutic heterogeneity may be present.2,3  In addition, ethnic disparities of all types may be accompanied by important social differences influencing medical access or diverse cultural practices with consequences for health care delivery and outcomes. It is therefore crucial to confirm conclusions about putative racial disparities with well-grounded assessments derived from large population–based data to avoid erroneous conclusions.

A recent review of previous small studies4-10  reported that the proportion of African American patients with immune thrombocytopenic purpura (ITP) was very low compared with the proportion of African Americans in the population. If that is the case, further investigation of environmental, social, and genetic factors that contribute would be a priority. However, if the report is not valid, not only will such investigations be fruitless, but negative social, economic, and public health consequences could result; for example, the level of suspicion for ITP in African Americans might be inappropriately low.

The cohort was identified from discharge records for inpatient hospitalizations at 142 nationwide Veterans Affairs (VA) hospitals between July 1, 1969, and September 30, 1996.11  The target population for calculation of ITP prevalence included all African American (N = 874 522) and white (N = 3 887 983) male veterans hospitalized at least once at age 18 or older (Table 1).

Table 1.

Characteristics of the study cohort: white and African American male veterans with at least one hospital admission between July 1, 1969, and September 30, 1996, who were followed more than 1 year



Whites

African Americans
Characteristics
Other than ITP
ITP
Other than ITP
ITP
No. of subjects   3 882 044   5 939   873 265   1257  
Mean age at study entry, y*  51.8   52.2   47.4   47.8  
Years of follow-up (mean)  11.6   5.5   11.9   6.0  
Person-y at risk  45 214 080   32 525   10 374 274   7484  
Mean age at ascertainment of ITP, y
 
NA
 
58.7
 
NA
 
54.8
 


Whites

African Americans
Characteristics
Other than ITP
ITP
Other than ITP
ITP
No. of subjects   3 882 044   5 939   873 265   1257  
Mean age at study entry, y*  51.8   52.2   47.4   47.8  
Years of follow-up (mean)  11.6   5.5   11.9   6.0  
Person-y at risk  45 214 080   32 525   10 374 274   7484  
Mean age at ascertainment of ITP, y
 
NA
 
58.7
 
NA
 
54.8
 

ITP indicates immune thrombocytopenic purpura (applied ICD-8 code: 287.1, ICD-9 code: 287.3); and NA, not applicable.

*

Age at first discharge record for inpatient hospitalization at Veterans Affairs hospitals between July 1, 1969, and September 30, 1996.

The first year of follow-up was censored.

Age-adjusted prevalence rates were directly standardized to the adult year 2000 United States standard population. Approval for these studies was obtained from the institutional review board of the National Institutes of Health (NIH). Informed consent was waived because we had no contact with study subjects.

We identified 1257 cases of ITP in African Americans and 5939 in whites (Table 1). Mean age at study entry for African American and white patients with ITP was 47.8 and 52.2 years, respectively. The age-adjusted prevalence for ITP was 189.3 (153.7-224.9, 95% confidence interval [CI]) per 100 000 for African Americans and 176.4 (161.5-191.3, 95% CI) per 100 000 for whites. The corresponding age-adjusted prevalence rate for ITP was 1.1-fold (0.9-1.3, 95% CI) higher in African Americans than in whites; the difference was not significant.

Our results indicate a similar age-adjusted prevalence of ITP among African Americans who were diagnosed in the hospital compared with whites and are in sharp contrast with previous small ITP studies.4-10  Our study's strengths include its large size (n = 7196) in a patient population with relatively stable and standardized access to medical care that is provided to veterans independent of ethnicity or socioeconomic status. Limitations include lack of detailed individual patient data, possible confounding due to differential utilization of services by race, and retrospective design derived from hospital discharge records, which potentially could bias our observations, since ITP usually does not lead to hospitalization. Since ITP is thought to be predominant in women, the restriction to male sex might limit the generalizability of our results. The varying specificity of applied ICD (International Classification of Diseases) codes over the 30-year study period would have resulted in inclusion of some subjects with thrombocytopenia other than ITP. However, the age-adjusted prevalence of ITP was assessed among African Americans and whites using the same hospital discharge registry, and such variations should be nondifferential between the 2 races.

In conclusion, we found little evidence of disparity in ITP prevalence among African American and white veterans.

Supported by the Intramural Research Program of the NIH, NCI.

O.L. and G.G. designed the study and obtained data; O.L., G.G., and T.R.F. analyzed data; all authors were involved in the interpretation of the results; O.L. initiated this work and wrote the report; all authors read, gave comments, and approved the final version of the manuscript; and all authors had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

The authors thank the Medical Administration Service of the Veterans Health Services and Research Administration, which provided the data on which this study is based, and Ms Heather Morris (Information Management Services, Silver Spring, MD) for assistance with data preparation.

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