Why It’s Difficult to Determine Exactly How Many People are Living with Lupus in the U.S.
The biggest challenge to determining how many people have lupus is first deciding on what constitutes a case of lupus. There are multiple forms of lupus with overlapping features – systemic lupus erythematosus (SLE), cutaneous lupus, drug-induced lupus, neonatal lupus, pediatric lupus, and late-onset lupus. There are subcategories for specific organ systems impacted by lupus, including discoid lupus, lupus nephritis, and neuropsychiatric lupus. And there are related syndromes that doctors believe are forms of lupus, including mixed connective tissue disease, undifferentiated connective tissue disease, and antiphospholipid antibody syndrome (APS).
There is no specific test to tell whether a person has lupus. No two lupus cases are precisely the same, making it hard to recognize and difficult to diagnose. Forty percent of people with lupus surveyed by the Lupus Foundation of America reported their doctor initially said they had some condition other than lupus, and 23 percent were told their problems were psychological, not physical.1
These factors contribute to the challenge of determining the exact incidence and prevalence rates for lupus among various populations in the United States.
History of Epidemiology Studies on Lupus
Over several decades, multiple epidemiological studies produced a 10-fold difference in incidence rates and a 12-fold difference in prevalence rates.2 These studies only included individuals that met specific classification criteria for systemic lupus erythematosus developed by the American College of Rheumatology (ACR) in 1982 and updated slightly in 1997. Cases also were limited to individuals treated at a medical center, potentially under-representing populations that might be at higher risk for developing lupus.
In 2004, the Lupus Foundation of America worked with Congress to establish population-based lupus registries through the U.S. Centers for Disease Control and Prevention (CDC). The goal was to determine the incidence and prevalence for all forms of lupus among all population groups most at risk for the disease in the United States.
The CDC funded registries were in select counties and regions in California, Georgia, Michigan, New York, and the Indian Health Services (IHS). The five registries represent the most extensive epidemiological study conducted in lupus to date. Georgia and Michigan published their data in 2013, the IHS in 2014, and California and New York in 2017.
In 2021, Izmirly et al. published a meta-analysis of the combined data from the five registries for cases that met the 1997 revised, yet stringent ACR classification criteria for systemic lupus erythematosus. Their analysis produced estimates for incidence and prevalence rates for systemic lupus erythematosus (SLE) among various population groups within the United States though noted a number of limitations to the study.
While data from the CDC-funded registries provide essential information about health disparities in lupus, it does not give a complete picture of the full scope and impact of lupus in the United States.
Is Lupus a Spectrum of Related Diseases?
There is a growing acceptance that lupus may not be a single disease but rather a spectrum of closely related disorders with overlapping causes, symptoms, and health effects. Systemic lupus erythematosus (SLE), on which the CDC-funded registries focused, represents only one slice of conditions grouped under the broader lupus umbrella. Limitations with the registries’ structure and methodology make it impossible to determine accurate rates for the incidence and prevalence of the full spectrum of lupus in the U.S.
These disease surveillance projects were monumental undertakings, professionally executed, and provide a number of key learnings toward improving our understanding of lupus. However, by relying on ACR criteria for case definitions and focusing exclusively on SLE, the five CDC-funded lupus registries significantly underestimate lupus's full impact in the United States.
CDC Registry Limitations:
Lupus is a complex disease which is further highlighted in the limitations noted in the CDC Registry Studies. Some limitations include:
- Technical Issues - The CDC Registry work was based on intensive retrospective chart reviews which was subject to missing data and illegibility of paper records.
- Stringent Classification Criteria - The stringent ACR SLE classification criteria used to identify cases of SLE is not a standard set of criteria used by doctors to diagnose lupus and potentially omitted as many as half of all lupus cases. A review of lupus patients at one major academic medical center in New York City found that only half of the patients receiving treatment for lupus fulfilled the ACR SLE classification criteria.3
- Skin Disease Not Included - The registries did not include cutaneous (skin) lupus. A study at a Minnesota medical institution found that the number of cutaneous lupus cases without systemic features (affecting the skin only) was equal to the number of systemic lupus cases. This study also found cutaneous lupus was three times more common among men and more prevalent among African Americans than previously understood.4 Since lupus is 3-4 times more common among African Americans, the incidence and prevalence among this group would likely be even higher than reported had cutaneous lupus been included across all five registry sites.
- Potential Sources for Lupus Cases - Not all medical providers within the surveillance areas were included in the study, potentially omitting many people with mild lupus whose cases were being managed by a primary care physician or other medical specialists.
CDC Registry Benefits:
Despite these limitations, the CDC registries have produced important information by illuminating the health disparities in lupus. Data highlights the disproportionate impact that lupus has on Blacks, Asians, Hispanics, Alaska Natives and American Indians compared to Whites.
The CDC has funded three ongoing cohort studies that will follow people with lupus over time to better understand the physical, emotional, social and economic impact of lupus.
Additional analysis of the data from the registries is illuminating the impact of lupus on specific organ systems, such as the skin, kidneys and connective tissue. Researchers have published several journal articles using data from the registries highlighting trends in diagnosis, treatment and comorbidity in lupus.
Lupus Foundation of America Estimate
Lacking definitive epidemiological data on lupus, in 1994 (and again in 1997 and 2000) the Lupus Foundation of America sponsored a national market research study, based on self-reported data, to ascertain the full impact of lupus on individuals, families and society in the United States. The Foundation estimates the number of Americans living with a form of lupus to be approximately 1.5 million. Learn how the Foundation arrived at this estimate. The Foundation regularly conducts surveys among people with lupus to highlight their urgent needs. These data support initiatives to bring greater attention and resources to research, education and services.
1 Lupus Foundation of America Patient and Caregiver Research Survey. Alan Newman Research. 2016
2 Lupus, the Chameleon: Many Disguises Difficult to Capture, Arthritis & Rheumatology. 2017. Vol. 69, No. 10, October 2017, pp 1921–1924. DOI 10.1002/art.40190
3 American College of Rheumatology Criteria for Systemic Lupus Erythematosus Exclude Half of All Systemic Lupus Erythematosus Patients, Arthritis & Rheumatology. 2017 Volume 69, Issue 7, doi.org/10.1002/art.40120.
4 Epidemiology of systemic lupus erythematosus and cutaneous lupus erythematosus in a predominantly white population in the United States, Arthritis Care and Research. 2015 May;67(6):817-28. DOI: 10.1002/acr.22502.