Validation of administrative data used for the diagnosis of upper gastrointestinal events following nonsteroidal anti‐inflammatory drug prescription

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Abstract
Summary Aims To validate veterans affairs (VA) administrative data for the diagnosis of nonsteroidal anti‐inflammatory drug (NSAID)‐related upper gastrointestinal events (UGIE) and to develop a diagnostic algorithm. Methods A retrospective study of veterans prescribed an NSAID as identified from the national pharmacy database merged with in‐patient and out‐patient data, followed by primary chart abstraction. Contingency tables were constructed to allow comparison with a random sample of patients prescribed an NSAID, but without UGIE. Multivariable logistic regression analysis was used to derive a predictive algorithm. Once derived, the algorithm was validated in a separate cohort of veterans. Results Of 906 patients, 606 had a diagnostic code for UGIE; 300 were a random subsample of 11 744 patients (control). Only 161 had a confirmed UGIE. The positive predictive value (PPV) of diagnostic codes was poor, but improved from 27% to 51% with the addition of endoscopic procedural codes. The strongest predictors of UGIE were an in‐patient ICD‐9 code for gastric ulcer, duodenal ulcer and haemorrhage combined with upper endoscopy. This algorithm had a PPV of 73% when limited to patients ≥65 years (c‐statistic 0.79). Validation of the algorithm revealed a PPV of 80% among patients with an overlapping NSAID prescription. Conclusions NSAID‐related UGIE can be assessed using VA administrative data. The optimal algorithm includes an in‐patient ICD‐9 code for gastric or duodenal ulcer and gastrointestinal bleeding combined with a procedural code for upper endoscopy.