Evaluation of the Completeness of ALS Case Ascertainment in the U.S. National ALS Registry: Application of the Capture-Recapture Method

Abstract

Introduction: The Centers for Disease Control and Prevention (CDC) National Amyotrophic Lateral Sclerosis (ALS) Registry is the first national registry for a chronic neurologic disease in the U.S. and uses a combination of case-finding methods including administrative healthcare data and patient self-registration. Methods: We applied capture-recapture methodology to estimate the completeness of the Registry for ascertaining patients with ALS for the first full year and the fourth years of the Registry (2011, 2014). The Registry uses the combination of two national administrative claims databases (Medicare and Veterans Affairs) with a self-register option at the registry portal. We conducted descriptive analyses of the demographic and clinical characteristics of the ALS cases identified by each of the sources and estimated the completeness of case ascertainment for each of the three ALS Registry sources individually, pairwise, and in all combinations. Results: Case-finding completeness was 54% in 2011 and improved to 56% in 2014. A smaller proportion of ALS patients under age 65 were ascertained than those 65 or older and ascertainment was also lower for non-White than White patients. The uncorrected ALS prevalence was 4.3/100,000 in 2011 (in 2014 5.0/100,000), but after correction for under-ascertainment, annual prevalence in 2011 was 7.9/100,000 (95% CI 7.6-8.2) (in 2014 was 8.9/100,000 (95% CI 8.7-9.2)). Discussion/Conclusion: Our findings indicate that administrative healthcare databases are a very efficient method for identifying the majority of ALS prevalent cases in the National ALS Registry and that the inclusion of a web registry portal for patients to self-register is important to ensure a more representative population for estimating ALS prevalence. Nonetheless, more than 40% of ALS cases were not ascertained by the Registry, with individuals younger than age 65 and people of color underrepresented. Recommendations are provided for additional methods that can be considered to improve the completeness of case ascertainment.