Background: A simple, effective and convenient method to assess dietary protein intake (DPI) for chronic kidney disease (CKD) patients is urgently needed in clinical practice. We developed a simple equation to evaluate DPI in patients with stage 3 CKD with the blood urea nitrogen (BUN)/serum creatinine (SCr) ratio (BUN/SCr).
Methods: In a prospective cohort of 136 inpatients with stage 3 CKD from 2 centres, 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.
Results: 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 validation and external validation indicated that model 5 resulted in the lowest values of bias and root mean square error and the highest P30 compared with model 3 and model 4. Therefore, the model 5 equation, DPI= -5.18 (-14.49 if the patient is female) +1.89×BMI+1.38×BUN/SCr, was selected because of the higher correlation [r = 0.498 (95% confidence interval 0.163,0.719)] and the smaller distribution of the difference between the predicted and measured protein intakes than those of the other models.
Conclusion: The DPI equation developed using BUN/SCr, sex and BMI may be used to estimate protein intake for patients with stage 3 CKD.
Trial registration
Chinese Clinical Trial Registry Center (ChiCTR-ROC-17011363). Registered in 11 May 2017, Retrospectively registered, http://www.chictr.org.cn/index.aspx