This is one of the most important questions about hospital readmissions. Some are unavoidable and warranted. Others are not. How much of each occur?’
A 2011 systematic review of the literature on this question was conducted by Carl van Walraven and colleagues (PDF) and published in the Canadian Medical Association Journal. They found large variation across studies in the proportion of readmission that are preventable (5%-79%), with a median of 27%. The almost certainly too-high upper value of 79% was reported by MedPAC in a 2007 Report to Congress (PDF, pages 107-108).
Van Walraven, et al. also found large variations in the methods employed by the 34 studies reviewed. They conclude,
Our study showed that the proportion of hospital readmissions deemed avoidable has yet to be reliably determined. Furthermore, we found a lack of consensus regarding the methods necessary to judge whether readmissions are avoidable. Given the large variation in the proportion of avoidable readmissions between studies using primary data, “avoidability” cannot accurately be inferred based on diagnostic codes for the index admission and the readmission. Instead, it needs to be determined through a peer-review process in which readmissions are classified as avoidable or not based on expert opinion.
Many of the same authors collaborated on an analysis of Ontario hospitals to calculate the proportion of readmissions that are preventable, published in the same year and journal.
The proportion of patients who had an urgent readmission varied significantly by hospital (range 7.5%– 22.5% ); the proportion of readmissions deemed avoidable did not show significant variation by hospital (range 1.2%– 3.7% ). [...] Urgent readmissions deemed potentially avoidable were relatively uncommon, comprising less than 20% of all urgent readmissions following hospital discharge.
The distribution of the probability that a readmission was avoidable is bimodal. An admission was either very likely not avoidable or very likely was, with hardly any ambiguity between.