Differences in clinical chemistry values according to the use of two laxatives for colonoscopy

Polyethylene glycol-electrolyte lavage solutions (PEG-ELSs) and sodium phosphate formulations (NaPs) are two major colon cleansing laxatives used in preparation for endoscopic examinations of the gastrointestinal tract. PEG-ELSs are osmotically balanced preparations, whereas NaPs are hyperosmotic purgatives. This study aimed to evaluate the effects of these two laxatives on routine chemistry tests.

We retrospectively reviewed 9366 clinical records of patients who had health checkups with or without colonoscopy from July 2010 to June 2011. We compared the values of 19 clinical chemistry parameters in the NaPs group (n=3239) and the PEG-ELSs group (n=1279) with those of controls (without colonoscopy, n=4848).

Compared with controls, the NaPs group had higher mean values of inorganic phosphate, sodium, chloride, creatinine, total protein, AST, and ALT, and lower mean values of calcium and potassium, exceeding acceptable biases. Notably, inorganic phosphate showed the largest % bias (51.14%). In the PEG-ELSs laxative group, higher mean values of inorganic phosphorus, creatinine, uric acid, AST, and total bilirubin and a lower mean value of potassium were observed compared with controls, exceeding acceptable biases. The effects of NaPs on inorganic phosphate, calcium, and electrolyte levels exceeded those of PEG-ELSs.

PEG-ELSs rather than NaPs are recommended as the first choice for bowel preparation, taking safety concerns and the reliability of laboratory values into account. Blood chemistry data from blood samples drawn after the ingestion of laxatives for colonoscopy should be interpreted with caution.