Abstract 165: Assessment of the Completeness and Accuracy of Case Ascertainment in the Michigan Stroke Registry
Authors: Reeves Mathew J , Nickles Adrienne , Roberts Stacey , Hurst Rochelle , Lyon-Callo Sarah 
Published: March 2022

Background-
Accurate case ascertainment by clinical registries is essential to obtain valid and representative data. Our aim was to assess the completeness and accuracy of case ascertainment in the Michigan Stroke Registry (MSR) - a member of the National Paul Coverdell Stroke Registry - by comparing its data to the Michigan Inpatient Database (MIDB) - a state-wide hospital discharge database.

Methods-
In 2009, 31 hospitals selected to be representative of all Michigan hospitals providing acute stroke care were enrolled in the MSR. Five hospitals that used in-hospital case sampling were excluded from this analysis. Cases of ischemic stroke (IS) in both the MSR and MIDB were identified using principle ICD-9 discharge codes: 433.x1, 434.x1, and 436. MSR cases were also limited to those with a final clinical IS diagnosis. Elective admissions for stroke related procedures were excluded from the MIDB. Cases in the two databases were then linked using a combination of hospital ID, age (years), sex, and admission date to identify unique stroke admissions. We regarded the MIDB as the gold standard; to assess the agreement in the number of stroke cases identified at each hospital we calculated the percent difference (PD) between the number entered in the MSR relative to the MIDB (PD = MSR-MIDB/MIDB) x 100%). To quantify the completeness of case ascertainment by MSR hospitals, we defined sensitivity as the proportion of IS cases identified by the MIDB that were matched to the MSR, and predictive value (PV) as the proportion of IS cases identified by the MSR that were matched to MIDB. We compared PD, sensitivity and PV according to the case ascertainment method used by each hospital (i.e., prospective, retrospective, or combination).

Results-
Overall, 23% fewer IS cases were entered into the MSR (n= 3443) compared to the MIDB (n= 4237, overall PD = -23.1%). Hospital-specific PDs varied widely from -600% to +10%, and 7 hospitals (27%) had large case undercounts of >40 cases (range 47 to 222). Eighty-seven percent (2984/3443) of MSR cases were successfully matched to the MIDB. MSR's overall sensitivity was 70.4% (2984/4237) but hospital-specific sensitivity rates varied widely (14% to 100%). MSR's overall PV was 86.7% (2984/3443) and hospital-specific PVs varied from 56% to 100%. Six hospitals using prospective case ascertainment had the highest overall sensitivity (75%, 95% CI = 73-77%), compared to 71% (95% CI = 69-73%) for the 9 sites using the combination approach, and 62% (95% CI = 59-65%) for the 11 sites using retrospective case ascertainment. However, one hospital in the retrospective group had a large undercount (222 cases); after it was excluded, sensitivity increased to 77% (95% CI-73-80%).

Conclusions-
Relative to hospital discharge data, hospitals participating in MSR missed almost ¼ of IS discharges. There was wide hospital-level variability in the completeness of case ascertainment; the majority of centers showed high agreement, but 27% of MSR hospitals showed substantial enough discrepancies to justify further investigation. These data illustrate the value of monitoring case ascertainment using comparable but external data sources.