Values for upper limit of normal should be given for liver enzymes^†

I read with great interest the article by Korman et al.,1 in which they demonstrated the high sensitivity and specificity of the ratios of serum alkaline phosphatase (ALP) to total bilirubin and the aspartate aminotransferase (AST) to alanine aminotransferase (ALT) as simple tools in the early diagnosis of Wilson disease in patients with acute liver failure. Reading the article, however, I could not find any mention of the upper limit of normal (ULN) for the ALP, AST, and ALT values used by the authors. Even if expressed in IU/L, these enzyme tests have widely different ULN depending on the commercial supplier of the respective kit. Indeed, the ULN for the ALP in adults may vary from 92-279 IU/L, the AST from 30-45 IU/L, and the ALT from 31-65 IU/L. Normal reference intervals of liver enzymes may also be affected by other factors such as sex, age, and ethnicity.2-4 Best known is the effect of age on serum ALP levels, with children and adolescents having much higher ULN than adults.5 For the above reasons, it would be most valuable to know the ULN of the liver enzymes used in the article by Korman et al., in order to apply their findings in our clinical practice.