Effects of Typical Bowel Preparation Dietary Restrictions on Serum Chemistry in Adult Subjects

Abstract

Introduction: Balanced electrolyte preparations such as PEG-ELS (GoLYTELY) or sulfate preps (SUPREP) are designed to minimize water and electrolyte movements. However, clinical studies often report statistically significant blood analyte deviations which are attributed to the preparation. Studies of bowel preparations have typically included non-fasting blood sampling for chemistry testing at a screening visit and then a second, fasting sample, after the bowel preparation has been consumed (immediately prior to colonoscopy). On the day prior to colonoscopy (after the screening visit), rigid dietary restrictions limiting patients to clear liquids are typically enforced to minimize the amount of solid feces required to be cleared by the bowel preparation. Limited data is available on the effect of this restrictive diet on serum chemistry values, and it is impractical for patients in large outpatient colonoscopy studies to return to the research center immediately before beginning their preparation for an additional blood draw. The current study was conducted to evaluate the impact of a typical pre-colonoscopy dietary regimen on the chemistry results of adults in the target demographic for colonoscopy.Table: Table. Mean Analyte Results by Sample (SD)Methods: 73 study subjects ages 50 to 75 were enrolled. Following informed consent, a non-fasting blood sample (“Screening Sample”) was collected for serum chemistry testing. Enrolled patients were given dietary instructions to follow on the day before their next visit (“Visit 2”). On the day prior to Visit 2 study subjects were permitted a light breakfast and then clear liquids for the rest of the day. Food and fluid ingestion was tracked by questionnaire. After midnight subjects were instructed to consume water only until they returned to the clinic the following morning and blood sample collection was complete. At Visit 2 a sample of blood for serum chemistry analysis was collected between 7-9am (“Fasting Sample 1”) and again four hours later (“Fasting Sample 2”). 60 subjects returned at Visit 2 for follow up blood sampling and are included in the data analysis. Fasting Sample results for each analyte were compared to their corresponding Screening Sample results by paired t-test. Results: A number of statistically significant changes in mean laboratory values were observed and are shown in the table. Anion gap seemed to be particularly sensitive where the number of patients with out of normal range anion gap increased from 8 at the Screening Visit, to 14 at Fasting Sample 1, and to 17 at Fasting Sample 2. Conclusion: The typical pre bowel preparation dietary regimen is associated with a number of statistically significant blood analyte changes independent of any bowel preparation. Especially marked changes in mean results are seen for amylase, anion gap, bicarbonate, BUN, protein, and bilirubin. Interpretation of clinical study laboratory results should account for this effect.