Studies using administrative hospitalization data often classify patients as having inflammatory arthritis based on diagnoses recorded at the hospitalization. We examined the agreement of these diagnoses with patients' prior medical histories.
We identified Medicare beneficiaries hospitalized in 2011 to 2015 for total hip arthroplasty (THA), total knee arthroplasty (TKA), acute myocardial infarction (AMI), or sepsis. We compared diagnoses of rheumatoid arthritis (RA) or ankylosing spondylitis (AS) at the index hospitalization to diagnoses over prior inpatient and outpatient claims. To assess the impact of potential misclassification, we compared hospital outcomes using the alternative methods of detecting beneficiaries with arthritis. Analyses were repeated using Medicaid data.
Among 506 781 Medicare beneficiaries with THA, 18282 had RA and 571 had AS at the arthroplasty hospitalization, while 13 212 had RA and 1519 had AS based on claims history. Diagnoses at the hospitalization were highly specific (0.98-0.99), but sensitivities (0.65 for RA; 0.31 for AS) and positive predictive values (PPV) (0.47 for RA; 0.83 for AS) were lower. For TKA, AMI, and sepsis, specificities were 0.97 to 0.99, sensitivities 0.60 to 0.66 for RA and 0.18 to 0.22 for AS, and PPVs 0.43 to 0.47 for RA and 0.73 to 0.77 for AS. In Medicaid, sensitivities were 0.21 to 0.67 for RA and 0.07 to 0.49 for AS. Frequencies of some hospital outcomes differed when arthritis was classified by the index hospitalization or claims history.
Diagnoses of RA and AS in hospitalization databases are highly specific but fail to identify large proportions of patients with these diagnoses.