Abstract
Objective
The APS ACTION Registry was created to study long-term outcomes in persistently antiphospholipid antibody (aPL)-positive patients. The objectives of this study were to examine the ethnoracial differences in clinical and laboratory characteristics of aPL-positive patients with no other systemic autoimmune rheumatic diseases (SARDs).
Methods
A web-based data capture system stores patient demographics and aPL-related medical history. Inclusion criteria are positive aPL results, based on the revised Sapporo APS classification criteria, tested at least twice within one year prior to enrollment. For this cross-sectional analysis of the baseline data, demographic, clinical, and laboratory characteristics of registry patients were analyzed based on self-reported ethnorace (White, Latin American Mestizo [LAM], Asian, and Black).
Results
728 patients with no history of other SARD (78% with APS classification) were included in the analysis. The ethnoracial distribution was 516 (78%) White, 82 (12%) LAM, 49 (7%) Asian, and 13 (2%) Black. Based on ethnoracial comparisons: (a) there were less females among White patients; (b) livedo reticularis/racemosa was more frequent in LAM patients; and (c) triple aPL positivity was more frequent in Whites, while isolated lupus anticoagulant positivity was more common in LAM patients.
Conclusion
In our international registry of persistently aPL-positive patients with or without APS classification, Blacks were the least frequently (2%) reported ethnoracial group. No major ethnoracial differences were found in the aPL-related clinical manifestations. Our analysis highlights the need for further investigation into the genetic and social determinants impacting the clinical and serologic phenotypes of aPL-positive patients across diverse populations.
Supplementary Information
The online version contains supplementary material available at 10.1186/s42358-026-00536-0.
Keywords: Antiphospholipid antibodies, Antiphospholipid syndrome, Anticardiolipin, Race, Ethnicity
Background
Antiphospholipid syndrome (APS) is an autoimmune disorder characterized by thrombosis and pregnancy morbidity in patients with persistently positive antiphospholipid antibodies (aPL) [1]. Although clinical presentation and treatment response vary among systemic lupus erythematosus (SLE) patients of different ethnoracial background [2], this variation, if it exists, has not been well characterized in aPL-positive patients without SLE or other systemic autoimmune rheumatic diseases (SARDs).
Ethnicity and race are distinct but interrelated concepts that play a critical role in understanding variations in disease presentation and outcomes. Ethnicity refers to the social and cultural characteristics, backgrounds, or experiences shared by a group of people, including language, religion, beliefs, values and behaviors that are often passed down through generations [3]. Race, on the other hand, is considered a social construct used to categorize people based on physical appearance, social factors and cultural backgrounds. Historically, racial classifications have been used to establish hierarchical systems that marginalize certain groups [4]. The current standard in the United States (US) for reporting race and ethnicity in clinical research is guided by the US Office of Management and Budget standards, which defines five racial categories: White, Black or African American, Asian, American Indian or Alaska Native, and Native Hawaiian or Other Pacific Islander, with Hispanic or Latino defined as an ethnicity category. These categories have not been updated since 1997, and there is growing recognition of the need for more granular and accurate data to address health disparities effectively [5].
The Antiphospholipid Syndrome Alliance for Clinical Trials and International Networking (APS ACTION) is an international network created to design and conduct large-scale, multicenter studies in persistently-aPL positive patients. The APS ACTION clinical database and repository (“Registry”), launched in 2012, is designed to investigate the natural course of persistently aPL-positive patients with or without other SARDs over a period of at least 10 years; patients from different regions of the world, i.e., Europe (EU), North America (NA) (US and Canada), Latin America (LA), and Asia-Pacific (AP), have been recruited in the registry [6].
The primary objective of this study was to investigate the ethnoracial distribution of persistently aPL-positive APS ACTION registry patients without other SARDs. In addition, we examined the demographic, clinical, and aPL differences among persistently aPL-positive patients of different ethnoracial backgrounds.
Methods
The APS ACTION registry includes adult patients who have had positive aPL based on the laboratory component of the Revised Sapporo Classification Criteria [7] at least twice within one year before enrollment. The patients are followed every 12 ± 3 months with clinical data and blood collection at enrollment and follow-up visits. A web-based data capture system is used to store patient demographics and aPL-related medical history.
For this cross-sectional analysis of the baseline data, demographic, clinical, and laboratory characteristics of registry patients with no other SARDs were compared according to self-reported ethnoracial background (White, Latin American Mestizo [LAM], Asian, and Black). Data captured from the registry included age, sex, ethnicity, history and type of macrovascular thrombosis, microvascular disease (aPL-nephropathy, diffuse alveolar hemorrhage, and livedoid vasculopathy), catastrophic APS, obstetric APS, and other APS manifestations (such as livedo, cardiac valve disease, immune thrombocytopenia, autoimmune hemolytic anemia, cognitive dysfunction and white matter changes), cardiovascular disease (CVD) risk factors, and aPL profile.
Descriptive statistics, Pearson’s chi-squared test, Fisher’s exact and Kruskal-Wallis tests were used for statistical analysis. Pairwise comparisons were performed using Bonferroni adjustment. To account for the six pairwise comparisons among the four ethnoracial groups, the Bonferroni-adjusted significance level was set at 0.0083.
Results
As of December 2023, 728 of 1,204 (61%) persistently aPL-positive registry patients had no history of SLE or other SARD, and 568/728 (78%) fulfilled the revised Sapporo APS classification criteria. The regional distribution of 728 patients was: 365 (50%) from Europe, 204 (28%) North America (US and Canada), 115 (16%) Latin America, and 44 (6%) Asia-Pacific. The demographic, clinical, and laboratory characteristics of aPL-positive patients by region are reported in Supplemental Tables 1 and 2.
The self-reported ethnoracial distribution of 660 patients was: 516 (78%) White, 82 (12%) LAM, 49 (7%) Asian, and 13 (2%) Black. Sixty-eight out of 728 patients were not included in the ethnoracial analysis due to missing information: (a) “not allowed to record” (n: 41 − 40 from Europe and 1 from Asia-Pacific), unknown (n:6 − 3 from North America, 2 from Latin America and 1 from Europe), or declined (n:1 -from North America); and (b) “other” background (n: 20 − 16 from North America and 4 from Europe). The demographic, clinical, and laboratory characteristics of aPL-positive patients by ethnoracial background are reported in Tables 1 and 2. In Asia, APS ACTION has participating centers only in China and Japan (39/49 of self-reported Asians). Median age was lowest in Asian patients (34, IQR: 30, 53) and highest in White patients (48, IQR 37, 58). There were less females among Whites (344/516, 67%) compared to LAM (70/82, 85%) (p = 0.001). There were no statistical differences in the frequency of macrovascular, microvascular, obstetric, and non-thrombotic aPL-manifestations across ethnoracial groups, except for livedo reticularis/racemosa, which was more frequent in LAM patients (18/82, 22%), compared to White (54/516, 11%) (p = 0.005). With respect to aPL profile, triple aPL-positivity was more frequent in White patients (203/516, 39%) compared to LAM (15/82, 18%) (p = 0.001), while single lupus anticoagulant positivity was more frequent in LAM (34/82, 42%) compared to Whites (125/516, 24%) (p = 0.01). Similarly, lupus anticoagulant positivity combined with either aCL or aβ2GPI (double positivity), was more frequent in LAM (19/82, 23%) compared to White patients (59/516, 11%) (p = 0.04). The frequency of baseline CVD risk factors did not differ significantly between groups, except for frequency of current or previous smoking (more frequent in White and LAM patients) and sedentary lifestyle (more frequent in LAM and Black patients) (Table 2).
Table 1.
Clinical and laboratory characteristics of antiphospholipid antibody-positive patients with no other systemic autoimmune rheumatic diseases by ethnoracial group
| Total | White | Latin American Mestizo | Asian | Black |
p
value |
|
|---|---|---|---|---|---|---|
| N: 660 | N: 516 | N: 82 | N: 49 | N: 13 | ||
| DEMOGRAPHICS | ||||||
| Median Age at Registry Consent (IQR) | 47 (36, 58) | 48 (37, 58) | 42 (34, 52) | 34 (30, 53) | 38 (37, 48) | 0.0001 |
| Female Sex (%) | 467 (71) | 344 (67)1 | 70 (85) | 42 (86) | 11 (85) | < 0.001 |
| CLINICAL PROFILE | ||||||
|
Macrovascular Thrombosis (Arterial and/or Venous) (%) |
430 (65) | 335 (65) | 62 (76) | 26 (53) | 7 (54) | 0.05 |
| Arterial Only (%) | 164 (25) | 124 (24) | 23 (28) | 14 (29) | 3 (23) | 0.80 |
| Venous Only (%) | 199 (30) | 158 (31) | 30 (37) | 8 (16) | 3 (23) | 0.09 |
| Arterial and Venous (%) | 67 (10) | 53 (10) | 9 (11) | 4 (8) | 1 (8) | 0.95 |
| Microvascular Disease (%) | 56 (9) | 42 (8) | 9 (11) | 4 (8) | 1 (8) | 0.86 |
| Catastrophic APS (CAPS) | 0.75 | |||||
| Definite CAPS (%) | 1 (0.2) | 1 (0.2) | 0 | 0 | 0 | |
| Probable CAPS (%) | 5 (0.8) | 5 (1) | 0 | 0 | 0 | |
| Obstetric APS | ||||||
| Any Pregnancy (% among females) | 327 (70) | 236 (69) | 57 (81) | 28 (67) | 6 (55) | < 0.001 |
| Pregnancy Morbidity (based on the Sapporo Criteria) + (%) | 215 (66) | 150 (64) | 43 (75) | 18 (64) | 4 (67) | 0.41 |
| Other APS Manifestations | ||||||
| Livedo reticularis/racemosa | 75 (11) | 54 (11) | 18 (22)2 | 3 (6) | 0 | 0.006 |
| Cardiac Valve Disease* (%) | 58 (11) | 47 (11) | 3 (4) | 8 (22)3 | 0 | 0.04 |
| Thrombocytopenia# (%) | 93 (14) | 73 (14) | 8 (10) | 10 (20) | 2 (15) | 0.41 |
| Autoimmune Hemolytic Anemia# (%) | 19 (3) | 15 (3) | 1 (1) | 3 (6) | 0 | 0.39 |
| Cognitive Dysfunction$ (%) | 22 (3) | 20 (4) | 1 (1) | 1 (2) | 0 | 0.52 |
| MRI White Matter Changes^ (%) | 116 (27) | 91 (26) | 14 (32) | 9 (30) | 2 (20) | 0.77 |
| ANTIPHOSPHOLIPID ANTIBODY PROFILE | ||||||
| Triple aPL-positivity (%) | 234 (36) | 203 (39)4 | 15 (18) | 13 (27) | 3 (23) | 0.001 |
|
Double aPL-positivity (%) LA-positivity with aCL or aβ2GPI (%) aCL and aβ2GPI (%) |
89 (14) 77 (12) |
59 (11) 65 (13) |
19 (23)4 5 (6) |
10 (20) 5 (10) |
1 (8) 2 (15) |
0.013 0.36 |
| Single aPL-positivity (LA) (%) | 175 (27) | 125 (24) | 34 (42)4 | 12 (25) | 4 (31) | 0.012 |
| Single aPL-positivity (aCL) (%) | 57 (9) | 40 (8) | 9 (11) | 5 (10) | 3 (23) | 0.2 |
| Single aPL-positivity (aβ2GPI) (%) | 27 (4) | 23 (5) | 0 | 4 (8) | 0 | 0.1 |
+Among females with history of pregnancy. *Among patients who had an echocardiogram. #Current or previous
$Neuropsychiatric test proven. ^Among patients who had a brain MRI
Statistically significant (ss) pairwise differences: 1White vs. Latin American Mestizo; 2Latin American Mestizo vs. White 3No ss difference is found in pairwise comparisons; 4White vs. Latin American Mestizo
APS: Antiphospholipid Syndrome, IQR: Interquartile Range, CAPS: Catastrophic Antiphospholipid Syndrome, MRI: Magnetic Resonance Imaging, aPL: antiphospholipid antibody, LA: Lupus Anticoagulant, aCL: Anticardiolipin Antibody, aβ2GPI: Anti-β2-Glycoprotein I
Table 2.
Frequency of cardiovascular disease risk factors among ethnoracial groups
| Total | White | Latin American Mestizo | Asian | Black | p value | |
|---|---|---|---|---|---|---|
| N: 660 | N: 516 | N: 82 | N: 49 | N: 13 | ||
| Hypertension (%) | 200 (30) | 154 (30) | 33 (40) | 9 (18) | 4 (31) | 0.07 |
| Hyperlipidemia (%) | 177 (27) | 148 (29) | 18 (22) | 8 (16) | 3 (23) | 0.2 |
| Diabetes (%) | 43 (7) | 35 (7) | 3 (4) | 3 (6) | 2 (15) | 0.4 |
| Current and Previous Smoking (%) | 234 (36) | 201 (39) | 28 (34) | 4 (8)1 | 1 (8) | < 0.001 |
| Chronic or End-Stage Renal Disease (%) | 24 (4) | 21 (4) | 3 (4) | 0 | 0 | 0.5 |
| Sedentary Lifestyle* (%) | 247 (37) | 176 (34) | 54 (66)2 | 8 (16) | 9 (69)2 | < 0.001 |
*Less than 30 min of daily exercise of any intensity
Statistically significant (ss) pairwise differences: 1Asian vs. White, Asian vs. Latin American Mestizo; 2Latin American Mestizo vs. White, Latin American Mestizo vs. Asian and Black vs. Asian
Discussion
In this cross-sectional analysis of a large international multicenter registry of persistently aPL-positive patients without other SARDs, individuals who self-identified as Black were the least frequently (2%) represented ethnoracial group. No significant differences were found in the frequency of aPL-related manifestations across ethnoracial groups, except for livedo reticularis/racemosa which was more frequent in LAM patients, compared to White patients. Triple aPL- positivity was more common in White patients, whereas lupus anticoagulant positivity (either isolated or in combination with aCL or aβ2GPI) was more frequent in LAM patients.
The incidence and prevalence of APS in the general population has been estimated to range between 1 and 2 cases per 100,000 and 40–50 per 100,000 respectively [8]. However, these estimates are challenged by the lack of standardized aPL testing, evolving classification criteria and expected disparities in the recognition and diagnosis of this rare disease. A targeted literature review estimated the incidence of APS in the US at approximately 7.1 to 13.7 per 100,000 person-years in the general population. However, the true incidence remains uncertain due to the diverse aPL-related clinical manifestations, inconsistent definitions of aPL positivity, under-recognition of the disease, and limited number of population-based studies, most of which do not account for ethnoracial distribution [9]. In one population-based cohort of patients with APS from 2000 to 2015 from Olmsted County, Minnesota, 97% (32/33) of patients with incident APS based on the Revised Sapporo APS Classification Criteria were White with only one patient identified as African American [10]. However, since the population of Olmsted County is predominantly White (86% based on 2010 U.S. Census data), these findings may not be generalizable to more ethnically diverse populations. Nevertheless, our study also demonstrated that Black patients were the least frequently represented ethnoracial group in the registry.
The low frequency of Black patients may indicate lower incidence of persistently positive aPL/primary APS in this group, or may indicate disparities in recruitment to the registry especially since there are no African participating centers. Another possibility is that Black patients may have a different aPL profile that does not meet the registry’s inclusion criteria. For example, IgA aCL and aβ2GPI have been reported as the most frequent isotype in African-Americans with APS (primary and secondary) in a small study of eight patients [11]. In patients with SLE and venous thrombotic events, African Americans were 66% less likely to have a clinically meaningful aPL profile compared to White patients [12]. Similarly, an analysis of the prevalence and racial distribution of strictly defined criteria aPL (lupus anticoagulant, and moderate-to-high titer aCL IgG/M and aβ2GPI IgG/M) across multiple prospectively collected longitudinal SLE cohorts showed that clinically meaningful levels of aCL and aβ2GPI IgG and IgM differed significantly among ethnoracial groups with lower frequency in Black patients [13].
There is a limited number of studies assessing differences in patients with persistently positive aPL and/or primary APS from various ethnoracial backgrounds and regions including Africa and the Middle East [14]. In a comparative study of patients with primary APS, 100 LAM from Colombia, Mexico, and Ecuador were compared to 538 White patients from the Euro-phospholipid cohort. Certain clinical manifestations such as transient global amnesia, pulmonary microthrombosis, arthralgias, early pregnancy losses were more common in LAM, whereas deep vein thrombosis, stroke, pulmonary embolism, thrombocytopenia, and anti-nuclear antibody (ANA) positivity was more frequent in Whites. There were no differences in frequency of IgM and IgG aCL and lupus anticoagulant positivity between the two groups [15]. More recent comparisons of Brazilian (88) vs. non-Brazilian (327) patients with primary APS using the APS ACTION registry have reported a higher frequency of non-white patients compared to white, higher frequency of livedo, cognitive dysfunction, seizures and lupus anticoagulant positivity, and a lower frequency of thrombocytopenia and positivity of aCL and aβ2GPI, as well as triple aPL positivity, in Brazilian patients [16]. A potential explanation for the observed differences, beyond genetic factors, may include environmental and socioeconomic influences, as well as disparities in access to healthcare. It is important to note that, in Brazil, intense admixture has decoupled skin color from genomic ancestry, meaning that self-identified or externally assigned racial categories may not accurately reflect individuals’ genetic backgrounds [17]. Consequently, in this study, there is a possibility that patients with African ancestry may have been misclassified as LAM. Our large-scale international study suggests that aPL-related manifestations were comparable across ethnoracial groups except for more frequent livedo reticularis/racemosa and LA positivity in LAM, and higher triple aPL-positivity in White.
With respect to the genetic component, in populations of European ancestry and primary APS, a genome-wide association study revealed two significant associations near HLA-DRA (within the HLA class II region) and STAT1-STAT4, among other loci contributing to genetic susceptibility to primary APS. Interestingly, cumulative genetic risk scores for primary APS were found to be highest in East Asian and African populations and lower in European and South Asian populations [18]. Although our study did not include genetic analyses, the findings may inform the design of future genetic investigation in diverse populations.
Limitations of our study include the potential for selection bias given that patients were recruited mainly from major referral medical centers where disease manifestations may be more complex and severe, and patients from certain ethnoracial groups may not accurately represent the general population. Additionally, the primary specialty of participating centers (e.g., hematology vs. rheumatology) may influence the types of clinical manifestations captured (e.g., thrombosis vs. microvascular disease). Another limitation is the self-reported nature of ethnoracial background which may lack granularity. Future studies using genetically determined ancestry may improve accuracy in patient categorization. Additionally, collection and inclusion of socioeconomic data is likely to provide a better understanding of patients’ background and their effect on health. Finally, our study did not include patients with APS and another SARD such as SLE but focused on primary APS and persistent aPL positivity without APS and other SARDs. Despite these limitations, strengths of this study are the large number of included patients from across the world, and the rigorous, standardized collection of clinical and laboratory data pertaining to persistently positive aPL, with or without APS. A future goal of APS ACTION includes collaboration with centers from underrepresented areas to better explore ethnoracial differences in patients with persistently positive aPL.
Conclusions
In summary, within the APS ACTION international registry of patients with persistently aPL-positive patients with or without APS classification, Black individuals represented the least frequently (2%) reported ethnoracial group, and no major differences in aPL-related clinical manifestations were observed across self-reported ethnoracial background. Future studies should focus on examining ethnoracial differences among patients with APS with or without SARDs and investigating the relevance of genetic ancestry and socioeconomic status in these patients. Efforts should also prioritize a diverse recruitment in patient cohorts and address barriers to participation in research in underrepresented populations.
Supplementary Information
Below is the link to the electronic supplementary material.
Acknowledgements
The APS ACTION Registry was created using REDCap provided by the Clinical and Translational Science Center at Weill Cornell Medical College (CTSC grant UL1 TR000457). We want to thank JoAnn Vega, CCRC, for her administrative support as the APS ACTION Global Lead Coordinator. We also want to thank all our APS ACTION Members: Guillermo Pons-Estel (Santa Fe, Argentina); Bill Giannakopoulos, Steve Krilis (Sydney, Australia); Guilherme de Jesus, Roger Levy, Flavio Signorelli (Rio de Janeiro, Brazil), Danieli Andrade, Gustavo Balbi (Sao Paulo, Brazil); Ann E. Clarke, Leslie Skeith (Calgary, Canada), Paul R. Fortin (Quebec City, Canada); Lanlan Ji, Zhouli Zhang (Beijing, China), Chengde Yang, Hui Shi (Shanghai, China); Cecile Yelnik (Lilly, France), Stephane Zuily, Denis Wahl (Nancy, France); Maria G. Tektonidou (Athens, Greece); Cecilia Nalli, Laura Andreoli, Angela Tincani (Brescia, Italy), Cecilia B. Chighizola, Maria Gerosa, Pierluigi Meroni (Milan, Italy), Vittorio Pengo (Padova, Italy), Giulia Pazzola (Reggio Emilia, Italy), Savino Sciascia, Silvia Foddai, Massimo Radin (Turin, Italy); Stacy Davis (Kingston, Jamaica); Olga Amengual, Tatsuya Atsumi (Sapporo, Japan); Imad Uthman (Beirut, Lebanon); Maarten Limper, Philip de Groot (Utrecht, The Netherlands); Guillermo Ruiz – Irastorza (Barakaldo, Spain), Ignasi Rodriguez-Pinto, Ricard Cervera, Jose Pardos-Gea (Barcelona, Spain), Esther Rodriguez Almaraz (Madrid, Spain), Maria Angeles Aguirre Zamorano, Chary Lopez-Pedrera (Cordoba, Spain); Bahar Artim-Esen (Istanbul, Turkey); Maria Laura Bertolaccini, Hannah Cohen, Maria Efthymiou, Ian Mackie (London, UK); Jason S. Knight, Yu Zuo (Ann Arbor, Michigan, US), Michelle Petri (Baltimore, Maryland, US), Rebecca K. Leaf (Boston, Massachusetts, US), Elena Gkrouzman (Worcester, Massachusetts, US), Robert Roubey (Chapel Hill, North Carolina, US), Thomas Ortel (Durham, North Carolina, US), Rohan Willis (Galveston, Texas, US), Nina Kello (New Hyde Park, New York, US), Michael Belmont, Medha Barbhaiya, Doruk Erkan, Steven Levine, Michael Lockshin, Jacob H. Rand, Jane Salmon (New York City, New York, US), Ali A. Duarte Garcia (Rochester, Minnesota, US), D. Ware Branch (Salt Lake City, Utah, US), and Nicola Pozzi (St Louis, MO, USA).
Author contributions
EG designed the study, analyzed and interpreted the data, wrote and substantially revised the manuscript. DE designed the study, acquired, analyzed and interpreted the data, and substantially revised the manuscript. DCOA designed the study, acquired and interpreted the data, and provided substantial revisions of the manuscript. AM and CB designed the study, interpreted the data, and provided substantial revisions of the manuscript. The rest of authors contributed their input in the design of the study, acquired data, and provided substantial revisions of the manuscript. All authors have approved the submitted version of the manuscript.
Funding
The APS ACTION Registry was created using REDCap provided by the Clinical and Translational Science Center at Weill Cornell Medical College (CTSC grant UL1 TR000457).
Data availability
The dataset used in this study is derived from the APS ACTION registry that supports multiple ongoing research projects. Due to confidentiality agreements and the potential impact on other studies, the data cannot be shared publicly. Reasonable requests for access may be considered by the registry’s governing body, subject to approval.
Declarations
Ethics approval and consent to participate
A written informed consent was obtained from all patients participating in the APS ACTION Registry. The Hospital for Special Surgery IRB (#2014 − 252) approved this study. The study was conducted in accordance with the Declaration of Helsinki.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Danieli Castro Oliveira de Andrade and Doruk Erkan Co-senior author
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
The dataset used in this study is derived from the APS ACTION registry that supports multiple ongoing research projects. Due to confidentiality agreements and the potential impact on other studies, the data cannot be shared publicly. Reasonable requests for access may be considered by the registry’s governing body, subject to approval.