Health examinees that underwent colonoscopy and blood tests on the same day at our center were included in this retrospective study. All subjects were prescribed either 2 L PEG plus AA or 4 L PEG for the bowel preparation prior to the colonoscopy. The incidences of electrolyte imbalance and renal impairment after colonic preparation were investigated. Renal impairment was determined if the subject's estimated glomerular filtration rate was measured less than 60 mL/min/1.73 m2.