The detection properties of enzymatic field effect transistors (EnFETs) based on pH-sensitive chemical field effect transistors (pH-ChemFETs) are modelled by taking into account the enzymatic reaction, the diffusion phenomena of the main chemical species in the electrolyte, the related acid/basic chemical reactions and the pH-ISFET potentiometric response. Thus, the pH distribution near the pH sensitive gate is characterized and the sensor detection properties have been studied as a function of the main analysis parameters. The modelling is developed for haemodialysis applications and more especially for the optimisation of urea-sensitive EnFETs. However, it is fully compatible with other EnFETs developments based on pH-ChemFET-metry.