Original Investigation Estimated GFR Decline Following Sodium Phosphate Enemas Versus Polyethylene Glycol for Screening Colonoscopy: A Retrospective Cohort Study

Background: Associations between sodium phosphate enemas and nephropathy have raised concerns about the safety of use as part of a bowel-cleansing regimen administered prior to colonoscopies. The objectives of this analysis are to evaluate the impact of sodium phosphate enema versus polyethylene glycol powder for oral solution (PEG) use prior to colonoscopy screening on estimated glomerular filtration rate (eGFR) decline in Veterans Affairs (VA) patients and identify other risk factors contributing to eGFR decline. Study Design: Retrospective cohort study. Setting & Participants: 70,499 VA patients receiving sodium phosphate enemas (with or without PEG) or PEG alone prior to colonoscopy screenings. Predictor: Use of either sodium phosphate or PEG. Outcomes: A 50% increase in serum creatinine level over a 15-month, over a 6-week, and between a 9- and 15-month period was used to define any, acute, or long-term eGFR decline, respectively. Measurements: Multivariable logistic regressions estimated the likelihood of eGFR decline conditional on the use of sodium phosphate enemas versus PEG alone, controlling for potential confounders. Results: A greater proportion of patients using sodium phosphate enemas versus PEG had any (P , 0.001) or long-term (P 5 0.003) eGFR declines, whereas similar proportions had acute eGFR declines (P 5 0.9). In the adjusted analyses, use of sodium phosphate enemas (6 PEG was associated with an increased likelihood of having any (OR, 1.3; 95% CI, 1.2-1.5) or long-term (OR, 1.4; 95% CI, 1.1-1.8) eGFR decline, but not acute eGFR decline (OR, 1.0; 95% CI, 0.6-1.7). Other risk factors for eGFR decline included diabetes and non–iron deficient anemia. Limitations: Unobserved heterogeneity due to volume depletion and potential selection bias due to higher-risk patients preferentially prescribed sodium phosphate enemas. Conclusions: Use of sodium phosphate enemas versus PEG alone prior to colonoscopy screening increases the risk for VA patients having long-term eGFR decline. Patients with non–iron deficient anemia are at particularly high risk for eGFR decline. These findings motivate the need to re-examine prescribing practices