Dear Sir,

We read with great interest the article by Yang et al. on biochemical predictors of common bile duct (CBD) stones [1], not least because we wrote a review article on the very same subject 15 years ago [2].

Obviously, the authors are to be congratulated on the enormous amount of data they have gathered on this interesting subject. Still, they have left us with some questions. First, since it is known that a combination of clinical and biochemical parameters increases the probability of CBD stones up to >90% [3], we wonder if it was specifically asked whether there were any signs of CBD obstruction (jaundice, light faeces, dark urine)? Second, since more than 7% of the patients did not undergo ultrasonography: was this not the first diagnostic imaging technique in the authors’ clinic in all cases, or were some patients asymptomatic? Third, for reasons of costs and radiation safety: why was the number of computed tomography (CT) scans so enormously high (almost one in every four patients)? This is especially interesting as the authors themselves state that this diagnostic tool is usually not recommended as the diagnostic modality of choice to predict absence or presence of CBD stones [1]. Finally, did the authors test the combination of more than twofold elevated total bilirubin and alkaline phosphatase as a predictor for CBD stones, which works well in our experience?