Objectives Idiopathic bile acid diarrhea (I-BAD) is a chronic condition involving debilitating diarrhea for some patients. Yet, the true prevalence is shrouded in uncertainty. It is often stated that I-BAD er grossly underdiagnosed and could possibly involve 1-2% of the general population. The literature within the field often claims that about 1/3 of diarrhea predominant irritable bowel syndrome cases are in fact misdiagnosed conditions of I-BAD. If this is the case, I-BAD can have significant, large-scale implications; from additional demands of new diagnostic procedures and treatments, to changes in patients’ perception of their circumstances. However, the evidence that is required to support the potential consequences that might follow is currently limited. We present the evidence behind the claims of I-BAD as well as the uncertainties involved and the risk of overdiagnosis.

Method We compared the scientific evidence within the field of I-BAD, with the few existing guidelines and expert papers on the topic. We then assessed the stated evidence with the principles of evidence-based medicine, including the standards for investigating and changing diagnostic criteria and procedures. We especially focused on potential mismatch between I-BAD expertise statements and the evidence that was used as support. Finally, we compared the findings with the concept of overdiagnosis, including the known drivers of overdiagnosis.

Results Preliminary results revolve around three core aspects of uncertainty pertaining to the underlying research: 1) the specifics of developing and validating the principal diagnostic method; 2) the body of evidence supporting the diagnostic method as whole; 3) and the methods to estimate the prevalence of I-BAD as well as its clinical use consequences. 1) The diagnostic method is based on validation efforts from the 1980’s, using very small populations sizes, the lack of a true reference standard, and extrapolation of results from a symptomatically similar, but pathologically dissimilar BAD subtype. 2) The evidence is heterogeneous and of generally poor methodological quality as pointed out by the National Institute for Health and Care Excellence. 3) Prevalence estimates are based on the prevalence of diarrhea predominant irritable bowel syndrome (IBS-D) which exhibit great variability both temporally and geographically, which in turn informs diagnostic accuracy metrics.

Conclusions I-BAD is a disabling disease that has recently been postulated to have a significantly higher prevalence than previously assumed. As this will have major implications for patients and the healthcare system, solid evidence is necessary. The preliminary results from our studies demonstrate a lack of evidence in this area as well as risks of overdiagnosis.