Validity of out-of-hospital and in-hospital cardiac arrest algorithms in the Danish National Patient Registry.

Aims: Cardiac arrest is registered in the Danish National Patient Registry (DNPR) with the International Classification of Diseases 10 revision code I46. However, it does not distinguish between out-of-hospital cardiac arrest (OHCA) and in-hospital cardiac arrest (IHCA). We validated an algorithm to identify cardiac arrest subtypes (out-of-hospital vs. in-hospital).

Methods: From Aarhus University Hospital, Denmark, we sampled patients with a primary or secondary cardiac arrest discharge diagnosis during 2019-2023. The algorithm categorized these patients as OHCA if they (1) only had a single department course during their hospitalization or (2) had multiple department courses during their hospitalization but were discharged with a cardiac arrest diagnosis from the first department course. The algorithm categorized the remaining patients as IHCA. We randomly sampled 200 patients with algorithm-based OHCA ( = 100) and IHCA ( = 100). Using medical record review as the reference, we calculated positive predictive values (PPVs) with 95% confidence intervals (CIs).

Results: Cardiac arrest was confirmed in 192 of 200 cases, yielding a PPV for cardiac arrest overall of 96% (95% CI: 92-98%). The PPV was 87% (95% CI: 79-92%) for OHCA and 61% (95% CI: 51-70%) for IHCA. The results were robust in age and sex strata.

Conclusions: The validity of a cardiac arrest diagnosis in the DNPR was overall high. The algorithm to distinguish cardiac arrest subtypes showed a high PPV for OHCA but a poor PPV for IHCA.