While beginning a registry for immune thrombocytopenic purpura (ITP) in Oklahoma, we noted that the number of black patients seemed smaller than expected. At the same time we read a report suggesting that ITP is rare among black Africans and people of African ancestry in other parts of the world.1  However, in standard textbooks and in major review articles on ITP, race is not mentioned. Therefore, we systematically searched the Medline database for all publications on ITP from the United States to identify articles describing 10 or more patients that identified patients by race; we found only 6 articles.2-7  These articles report data from different regions of the United States and across many years.

In each of the 6 articles,2-7  the proportion of blacks among patients with ITP was lower than the proportion of blacks in the population (Table 1). In 5 of the published studies, the 95% confidence interval (CI) for the observed percent of blacks among the ITP patients did not overlap with the percentage of blacks in the population.2-4,6,7  One of these articles commented on their observation that only 4 (6%) of 67 patients with ITP were black, compared with 25% of their hospital patients.2 

Table 1.

Frequency of blacks among patients with immune thrombocytopenic purpura





Patients

Study (site)
Publication y
Y of patient accrual
Total, no.
Black, no. (%, 95% CI)
% black*
Block et al2  (Chicago)  1966   1948-1964   67   4 (6.0, 1.7-14.6)   24.3  
Wilde et al3  (Pittsburgh)  1967   1949-1966   43   2 (4.7, 0.6-15.8)   16.7  
Akwari et al4  (Durham)§  1987   1975-1985   100   20 (20.0, 12.7-29.2)   47.1  
Guthrie et al5  (Augusta)  1988   1954-1983   40   12 (30.0, 16.6-46.5)   37.4  
George et al6  (United States)  2003   1997-2000   66   5 (7.6, 2.5-16.8)   18.1  
Aledort et al7  (United States)**  2004   2000-2001   158   9 (5.7, 2.6-10.5)   24.8  
Unpublished review (Oklahoma)††
 
2004
 
2004
 
87
 
4 (4.6, 1.3-11.4)
 
8.0
 




Patients

Study (site)
Publication y
Y of patient accrual
Total, no.
Black, no. (%, 95% CI)
% black*
Block et al2  (Chicago)  1966   1948-1964   67   4 (6.0, 1.7-14.6)   24.3  
Wilde et al3  (Pittsburgh)  1967   1949-1966   43   2 (4.7, 0.6-15.8)   16.7  
Akwari et al4  (Durham)§  1987   1975-1985   100   20 (20.0, 12.7-29.2)   47.1  
Guthrie et al5  (Augusta)  1988   1954-1983   40   12 (30.0, 16.6-46.5)   37.4  
George et al6  (United States)  2003   1997-2000   66   5 (7.6, 2.5-16.8)   18.1  
Aledort et al7  (United States)**  2004   2000-2001   158   9 (5.7, 2.6-10.5)   24.8  
Unpublished review (Oklahoma)††
 
2004
 
2004
 
87
 
4 (4.6, 1.3-11.4)
 
8.0
 

Data summary for all published articles from the United States describing 10 or more patients that identified patients by race.

*

Census data are percentages for one race reported as black non-Hispanic

Census data for Chicago for 1960 were obtained from the Reference Department of the Illinois State Library, Springfield, IL

Census data for Pittsburgh for 1960 were obtained from the Bureau of State Library-Law/Government Publication, State Library of Pennsylvania, Harrisburg, PA

§

Census data for Durham for 1980 were obtained from the Missouri State Census Data Center (http://oseda.missouri.edu/mscdc/census/us/trend/places/S37NC/P370|750), August 17, 2004

Census data for Richmond County, which includes Augusta, for 1980 were obtained from the East Central Georgia Regional Library, Augusta, GA

This study reported 70 adult patients, ages ≥ 18 years, from 20 United States' sites that enrolled 1 to 10 patients. The 4 patients from our site are omitted to avoid analysis of duplicate patients; they are included in our Oklahoma data. Census data for adults ages ≥ 18 years were obtained from the United States Census Bureau; Census 2000, PL 94-171 Summary File, using American Fact Finder; http://factfinder.census.gov (July 27, 2004). Data for the cities where the studies were performed were averaged in proportion to the number of patients enrolled from each city. Data on race were not included in the published article6  but were obtained from the original case report forms

**

This study reported data on race for 185 adult patients, ages ≥ 18 years, from 11 sites that enrolled 4 to 46 patients. The 4 patients from our site are omitted to avoid analysis of duplicate patients; they are included in our Oklahoma data. The 23 patients from Canada also are omitted since this analysis is limited to the United States census data for adults ages ≥ 18 years that were obtained from the United States Census Bureau; Census 2000, PL 94-171 Summary File, using American Fact Finder; http://factfinder.census.gov (July 27, 2004). Data for the cities where the studies were performed were averaged in proportion to the number of patients enrolled from each city. Data from the individual sites were not included in the published article7  but were obtained from Amgen, Thousand Oaks, CA

††

Unpublished data from our record review to begin an Oklahoma ITP Registry. Census data were obtained from the United States Census Bureau; Census 2000 Summary File 1; using American Fact Finder; http://factfinder.census.gov (August 16, 2004). Data for individual Oklahoma counties were averaged in proportion to the number of patients living in each county

A potential limitation of this study is our selection of census data. Although our calculations were based on United States census data for the cities from which the patients were reported and from a time near to patient accrual (Table 1), the percentage of blacks in the census data that we used may not accurately reflect the geographic origin of the reported patients if referral areas were large.

Our awareness of potential racial disparities was stimulated by our recent demonstration, from the Oklahoma Thrombotic Thrombocytopenic Purpura Hemolytic Uremic Syndrome (TTP-HUS) Registry, of an increased proportion of blacks among patients with TTP and severe ADAMTS13 deficiency. The age- and sex-standardized incidence rate ratio of blacks to nonblacks was 9.3 (95% CI, 4.3-19.9).8  The apparent opposite racial disparity among patients with ITP and TTP is intriguing, but different racial disparities also occur among other autoimmune disorders. For example, the prevalence of systemic lupus erythematosus (SLE) is greater among blacks,9  while the prevalence of anticardiolipin antibodies preceding SLE is greater among whites.10 

If a racial disparity among patients with ITP is confirmed, it may indicate a genetic influence on the etiology of ITP. Alternative explanations may be that the diagnosis of ITP is made less often among blacks because of disparities in health care11  or because the presence of petechiae and ecchymoses may not be appreciated.

1
Salawu L, Durosinmi MA. Immune thrombocytopenic purpura: 11-year experience in Ile-Ife, Nigeria.
African J Med Med Sci
.
2001
;
30
:
99
-103.
2
Block GE, Evans R, Zajtchuk R. Splenectomy for idiopathic thrombocytopenic purpura.
Arch Surg
.
1966
;
92
:
484
-489.
3
Wilde RC, Ellis LD, Cooper WM. Splenectomy for chronic idiopathic thrombocytopenic purpura.
Arch Surg
.
1967
;
95
:
344
-350.
4
Akwari OE, Itani KMF, Coleman RE, Rosse WF. Splenectomy for primary and recurrent immune thrombocytopenic purpura.
Ann Surg
.
1987
;
206
:
529
-541.
5
Guthrie TH, Brannan DP, Prisant LM. Idiopathic thrombocytopenic purpura in the older adult patient.
Amer J Med Sci
.
1988
;
296
:
17
-21.
6
George JN, Raskob GE, Vesely SK, et al. Initial management of immune thrombocytopenic purpura in adults: a randomized controlled trial comparing intermittent anti-D with routine care.
Amer J Hematol
.
2003
;
74
:
161
-169.
7
Aledort L, Hayward CPM, Chen M-G, Nichol J, Bussel J. Prospective screening of 205 patients with ITP, including diagnosis, serological markers, and the relationship between platelet counts, endogenous thrombopoietin, and circulating antithrombopoietin antibodies.
Amer J Hematol
.
2004
;
76
:
205
-213.
8
Williams LA, Terrell DR, Lammle B, et al. The incidence of TTP-HUS: racial disparity among patients with severe ADAMTS13 deficiency [abstract].
Blood
.
2004
;
104
:Abstract 857.
9
McCarty DJ, Manzi S, Medsger TA Jr, et al. Incidence of systemic lupus erythematosus: race and gender differences.
Arthritis Rheum
.
1995
;
38
:
1260
-1276.
10
McClain MT, Arbuckle MR, Heinlen LD, et al. The prevalence, onset, and clinical significance of antiphospholipid antibodies prior to the diagnosis of systemic lupus erythematosus.
Arthritis Rheum
.
2004
;
50
:
1226
-1232.
11
Bach PB, Pham HH, Schrag D, Tate RC, Hargraves JL. Primary care physicians who treat blacks and whites.
N Eng J Med
.
2004
;
351
:
575
-584.