Development and Validation of a National US Achalasia Cohort: The Veterans Affairs Achalasia Cohort (VA-AC)

Abstract

Achalasia is an esophageal motility disorder associated with significant morbidity, yet achalasia-associated risk factors and outcomes are not well-characterized. Our aim was to establish a national cohort of individuals with achalasia, utilizing Veterans Health Administration (VHA) data. We iteratively developed combinations of International Classification of Diseases and Current Procedural Terminology code algorithms to validate an approach for identifying achalasia cases. We assessed algorithm accuracy for achalasia diagnosis through manual chart review of candidate achalasia cases and candidate non-achalasia controls. The prespecified end point chosen to establish algorithm performance success was achieving a 1-sided 95% confidence lower bound for a positive predictive value >85% for a random sample of 100 candidate achalasia cases. Once adequate performance was validated, we queried national VHA data to establish and characterize a cohort of individuals diagnosed with achalasia between 1999 and2020. Three rounds of algorithm modification and validation were conducted to achieve the prespecified performance endpoint. In the final round, a combination of 3 or more International Classification of Diseases codes for achalasia in the subject's lifetime and a Current Procedural Terminology code for esophageal manometry achieved an observed 94% positive predictive value (1-sided 95% confidence lower bound of 88.5%) for identifying achalasia. Applying the algorithm to national VHA data identified a cohort of 2100 individuals with achalasia, with a median age 65 years and who were 93% male. Using a rigorous validation approach, we established a national cohort of 2100 individuals with achalasia within the VHA, one of the largest established to date. This cohort can be utilized to study risk factors for achalasia and outcomes over time.