Do discharge codes underestimate hospitalisation due to heart failure? Validation study of hospital discharge coding for heart failure.

BACKGROUND: Discharge codes are frequently used to describe hospital activity related to heart failure (HF).
OBJECTIVES: To determine whether discharge codes for HF underestimated or overestimated hospital activity related to HF.
DESIGN: Patients with atrial fibrillation (AF), who commonly have HF, were identified and their case notes reviewed to identify cases of HF missed by discharge codes. PARTICIPANTS AND METHODS: Patients admitted between November 1997 and January 1998 with either HF or AF. Identification of HF and AF by ICD10 hospital discharge codes. Identification of additional cases of AF from a central hospital-wide ECG database.
RESULTS: We identified 330 cases with an ICD 10 code for HF, of which 43 (13%) were deemed to be miscoded, 32 patients (10%) were classified as possible, 39 (12%) as probable and 216 (65%) as definite HF. Results were similar whether or not HF was the primary discharge diagnosis. We identified 452 patients with AF, of whom 45 (10%) were classified as probable and 193 (43%) as definite HF. 129 (54%) of these cases had no diagnostic discharge code for HF. ICD 10 discharge codes for HF were correct in 77% of cases but identified only 66% of patients with probable or definite HF in this analysis. Screening of other diagnoses would have identified further cases of HF.
CONCLUSIONS: Hospital discharge codes substantially underestimate hospital events related to HF in the UK.