Category: Clinical Stones: Medical Management

MP10-20 - Development of A Predictive Model to Estimate Success Rates of Conservative Dietary Management on 24-hour Urinary pH in Stone Formers

Fri, Sep 21
2:00 PM - 4:00 PM

Introduction & Objective : Low urine pH is often cited as a risk factor for formation of both calcium oxalate and uric acid stones. While urinary alkilization is the cornerstone of pharmacologic management, patients often prefer dietary modification over medication. We sought to assess and predict changes in urinary pH associated with dietary management in the absence of directed alkali medical therapy.


Methods : We performed a retrospective cohort study of stone formers seen from 2000-2015 with multiple 24-hour urine analyses (24UA). Patients over 17 with multiple 24UAs and a baseline low urine pH (< 6.0) were included and those treated with thiazide diuretics or alkalinizing agents were excluded. Race, age, sex, BMI, 24UA parameters, and medications were abstracted. Gastrointestinal alkali absorption (GIAA) was calculated from 24UA data. Primary outcome was favorable urine pH (pH > 6.0) on second 24UA. Potential predictors were selected into a multivariable logistic regression model using a modified stepwise procedure in R.


Results : We identified 2197 kidney stone formers; 224 patients met inclusion criteria. On second 24UA, 124 (55.4%) reached a favorable pH. On univariate analysis a favorable second pH was associated with higher initial pH, low initial sulfate, young age, increase in citrate, decrease in ammonium, increase in GIAA, and increase in urine volume (all p < 0.02). On multivariable analysis, higher initial pH (OR=23.64, P<0.001), decrease in ammonium (OR=0.16, P<0.001), increase in GIAA (OR=7.34, P<0.001), increase in urine volume (OR=2.08, P=0.001), lower initial sulfate (OR=0.96, P=0.001), high initial GIAA (OR=1.03, P=0.005), and increase in citrate (OR=2.21, P=0.04) were associated with a favorable second pH. ROC curve for the multivariable predictive model demonstrated a corrected AUC of 0.844 (Figure 1).


Conclusions : Our data suggest that dietary recommendations, specifically increases in fluid intake, citrate, GIAA, and decrease in acid load, may suffice to improve urinary pH in certain patients. Our model may be used to counsel patients on the possibility of successfully increasing urine pH with conservative dietary modification alone and aid in determining if pharmacologic management is required.

Brenton B. Winship

Endourology Fellow
Duke University Medical Center, Division of Urology
Durham, North Carolina

Daniel Wollin

Durham, North Carolina

Leah Davis

Durham, North Carolina

Evan Carlos

Durham, North Carolina

Russell S. Terry

Endourology Fellow
Duke University Medical Center, Division of Urology
Durham, North Carolina

Fellow in Endourology, Metabolic Stone Disease, Laparoscopy, and Robotic Surgery
Division of Urologic Surgery
Duke University Medical Center

John Asplin

Medical Director
Litholink Corporation
Chicago, Illinois

Charles D. Scales

Associate Professor
Duke University Medical Center, Division of Urology
Durham, North Carolina

Charles D. Scales, Jr., MD MSHS is Associate Professor of Surgery (Urology) and Population Health at Duke University School of Medicine and Vice Chief for Quality Improvement and Patient Safety in the Division of Urologic Surgery. He completed medical school and residency training in urology at Duke University Medical Center. After residency, Dr. Scales completed the Robert Wood Johnson Foundation Clinical Scholars Program at UCLA, where he received advanced training in health services research, health policy, and quality of care.

Dr. Scales has a strong interest in education, having previously served on the ACGME Review Committee for Urology and as a member of the ACGME Board of Directors. He currently leads a course in quality improvement and data analytics in the Masters of Management in Clinical Informatics program at the Duke University School of Medicine.

From the research perspective, Dr. Scales has a longstanding interest in the epidemiology of and patient care for urinary stone disease. Recent studies have redefined the burden of urinary stone disease in the United States, compared the effectiveness of dominant stone removal technologies, and identified new opportunities for improving patient-centered and policy-relevant outcomes, such as unplanned care after procedural interventions. His research and perspective on urinary stone disease has been highlighted in U.S. News & World Report, Reuters, NPR, and the Wall Street Journal, among other media outlets.

As a result of these investigations, he has an appointment at the Duke Clinical Research Institute where he leads a diverse health services and clinical research program. He has received research support from the National Institute of Aging, the American Geriatrics Society, and philanthropic funding, among other sources. Currently, Dr. Scales is the Principal Investigator for the Scientific Data and Research Center for the NIDDK Urinary Stone Disease Research Network (U01).

Michael Ferrandino

Assoc Professor of Urology Surgery
Duke University Medical Center
Durham, North Carolina

Dr. Michael Ferrandino is Director of Minimally Invasive Surgery for the Division of Urology at Duke University Medical Center in Durham, NC. He is an Associate Professor of Urologic Surgery. His area of expertise and is minimally invasive surgical approaches to benign and malignant urologic disease. He received his medical degree in 2001 from NYU School of Medicine. In 2007 he completed his urology residency at SUNY Downstate Medical Center and went on to an Endourologic Fellowship at Duke University Medical Center. He joined the faculty after fellowship and has continued to grow the field of minimally invasive surgery throughout his tenure. He serves as the Associate Residency Program Director and the Vice Chief of Education for the Division of Urology.

Glenn M. Preminger

Duke University Medical Center, Division of Urology
Durham, North Carolina

Michael E. Lipkin

Associate Professor Urology
Duke University Medical Center, Division of Urology
Durham, North Carolina