Development and validation of a simple equation to evaluate dietary protein intake using the blood urea nitrogen/serum creatinine ratio in patients with stage 3 chronic kidney disease

Abstract

The aim of this research was to develop a simple equation to evaluate dietary protein intake (DPI) in patients with stage 3 chronic kidney disease (CKD) using the blood urea nitrogen (BUN)/serum creatinine (SCr) ratio (BUN/SCr). In a prospective cohort of 136 inpatients with stage 3 CKD from 2 centres, the estimated dietary protein intake (DPI) was calculated using Maroni’s formula after the patients implemented a 7 day protein-restricted diet. We developed estimation equations based on BUN/SCr and the spot urinary urea nitrogen (UUN)/urinary creatinine (UCr) ratio (UUN/UCr) in combination with sex and body mass index (BMI). These equations were then internally and externally validated. The following candidate parameters were derived from univariate regression analysis for 5 established models: sex, BMI, BUN/SCr, UUN and UUN/UCr. Sex and BMI were included in all models after variable evaluation using multiple regression analysis. UUN, UUN/UCr and BUN/SCr were included in model 3, model 4 and model 5, respectively. Both internal and external validation indicated that model 5 resulted in the lowest values for bias and root mean square error and the highest P30 compared with model 3 and model 4. Therefore, the model 5 equation, DPI\u2009=\u2009\u2009−\u20095.18 (−\u200914.49 if the patient is female)\u2009+\u20091.89\u2009×\u2009BMI\u2009+\u20091.38\u2009×\u2009BUN/SCr, was selected because of the higher correlation (r\u2009=\u20090.498) between the estimated DPI and predicted DPI. The DPI equation developed using BUN/SCr, sex and BMI may be used to estimate protein intake for patients with stage 3 CKD. Chinese Clinical Trial Registry Center (ChiCTR-ROC-17011363). Registered on 11 May 2017, Retrospectively registered, http://www.chictr.org.cn/index.aspx.