Background/Purpose: Routine data sources such as death certificates are used to estimate the burden or cost of disease in a population. However, mortality due to rare diseases, e.g., systemic lupus erythematosus (SLE), that are significant sources of premature mortality, is often ignored in mortality reports. The objective of this study was to determine the completeness of SLE mention in the death register in Sweden and patterns of completeness by demographic factors.

Methods: A Swedish population-based cohort of individuals with prevalent SLE (the Swedish Lupus Linkage [SLINK]; 2001-2013) was linked to the Cause of Death Register. All death records from subjects known to be deceased in the cohort were reviewed and information regarding patient demographics (i.e., sex, age, region, place, and year of death) and causes of death were extracted. Odds ratios (OR) and 95% confidence intervals (95% CI) for the absence of SLE on death certificates were estimated using a multivariable-adjusted logistic model. We also estimated the degree of over- or underestimated SLE mortality using the comparability ratio.

Results: Approximately 59% of decedents with SLE had SLE absent from their death certificates (n=1,802). The majority of deceased individuals were aged 60-79 years at death (52%), female (81%), and born in Nordic countries (96%). In the adjusted model, increasing age was associated with SLE being absent from death certificates among those in the established cohort. Decedents 60-79 years old at death were approximately 2.5 times as likely to have SLE missing from their death certificates compared with those <40 years (OR: 2.48, 95% CI: 1.34-4.58). Having renal failure listed on the death certificate decreased the likelihood of SLE being absent (OR: 0.55, 95% CI: 0.41-0.73), while cancer increased this likelihood (OR: 2.35, 95% CI: 1.83-3.02). Death certificate data underestimated SLE mortality by 59% (comparability ratio 0.41 [95% 0.38-0.43]).

Conclusion: SLE is greatly underreported as a cause of death on death certificates thereby underestimating the burden of this disease. This may be due to ambiguity and disparate practices concerning the recording of comorbidities in death certificates. Inadequate attention may be devoted to the contribution of lupus to cancer secondary to systemic inflammation compared to lupus mortality related to direct organ involvement.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/do-death-certificates-underestimate-the-burden-of-rare-diseases-the-example-of-systemic-lupus-erythematosus-mortality-in-sweden/