Diagnostics and treatment of pancreatic exocrine insufficiency: clinical guidelines of the Russian gastroenterological association - V. T. Ivashkin; I. V. Mayev; A. V. Okhlobystin; S. A. Alekseyenko; Ye. V. Beloborodova; Yu. A. Kucheryavy; T. L. Lapina; A. S. Trukhmanov; I. B. Khlynov; M. V. Chikunova; A. A. Sheptulin; O. S. Shifrin (Российский журнал гастроэнтерологии, гепатологии, колопроктологии, 2018)