Our review demonstrated high variation in the validity of administrative data for recording HF. The sensitivity and PPV ranged widely, but specificity and NPV were substantially high across studies. This suggests that the validity of administrative data should be considered before analyzing and interpreting results. Differences in validity can be explained by factors related to ICD coding systems, organization, coder’s experience, reference standards and type of administrative database.
The validity of administrative data is extremely important given the increased use of these data for surveillance and outcome research. For population surveillance, those admitted to the hospital with HF will most likely represent severe cases of the disease in the late stages of the diagnosis; therefore, relying solely on the HF-defining ICD codes (428 or I50) in hospital discharge data will underestimate the prevalence of disease (32
). For the majority of studies reviewed, hospital discharge data were the primary administrative data source used for validation. More research is needed to examine the validity of outpatient or community data for population surveillance.
More than 70 ICD-8, -9 and -10 codes were used to define HF across the validation studies. The European Cardiovascular Indicators Surveillance Set (EUROCISS) project (34
) suggests that validation studies on HF should consider ICD codes for HF, hypertensive heart, other primary cardiomyopathies, alcoholic cardiomyopathy, secondary cardiomyopathy and chronic cor pulmonale. However, ICD-9 code 428 and ICD-10 code I50 accounted for the majority of HF cases in the Canadian hospital discharge data, and other codes had a smaller impact on the prevalence. However, the impact of each code on HF outcomes should be evaluated in the future.
We noticed that the prevalence of HF differed between ICD-9 and ICD-10 data. There are several potential explanations for this difference, possibly related to the learning curve from ICD-9 to the new coding system ICD-10, the declining incidence of HF in that period or improved HF outpatient management. Quan et al (19
) evaluated the validity of HF and found little impact of the coding system change from ICD-9 to ICD-10 on HF validity in Canadian data (sensitivity 71.6% in ICD-9 and 68.6% in ICD-10; PPV 90.5% in ICD-9 and 90.2% in ICD-10).
We found that of nine Canadian studies, six demonstrated high PPV estimates (greater than 85%) and two studies reported PPV values of 51% and 65%. The variation can be partially explained by the variation in reference standards for validating HF across studies. Some studies used HF recorded in the patient’s chart as a reference standard, while other studies defined HF based on clinical or diagnostic evidence in the chart. Studies that relied on chart documentation of HF are likely to produce higher sensitivity values but lower PPVs than those that defined HF using a consistent clinical definition (Framingham, NYHA, Boston and ESC criteria). However, previous studies (35
) have shown that clinical information is often missing in the patient chart, which can leave the diagnosis questionable. Furthermore, many countries have shown that diagnostic tests are not consistently conducted in all patients with suspected HF (38
). Diagnosis of HF is challenging, and cases can be misclassified under other diseases because symptoms can be nonspecific to HF, particularly in the elderly (39
Various administrative data definitions were used to define HF across studies, and this can explain much of the variability across the results. For example, many studies used a variety of ICD codes to define HF with ICD-9 and -10 codes 428 and I50 as the only codes being consistently applied across all studies. Some studies (10
) defined HF using the principal/most responsible/major diagnosis alone. Using this method meant including patients with HF who were severe enough to be hospitalized or whose HF contributed to the length of stay most likely to generate high PPV estimates. Other studies (16
) defined HF using all available diagnosis coding fields, resulting in inclusion of patients with HF as a comorbidity or complication. HF is likely to be under coded when HF is present as a comorbidity (ie, it does not contribute to length of stay significantly), which likely generates low PPV estimates.