MO022URINARY PHOSPHATE/UREA RATIO, A NEW TOOL TO EVALUATE ADHERENCE TO PHOSPHATE DIETARY INTERVENTIONS IN CKD PATIENTS

Background and Aims In chronic kidney disease (CKD) patients, phosphate (P) restriction is crucial for the control of mineral metabolism. Many reports indicate that P intake doesnot correlate with 24-hour phosphaturia. Different sources of P (organic or inorganic) have different intestinal absorption rates. Different proportions of organic and inorganic P in diet might be the reason for the lack of correlation between phosphorus intake and phosphaturia. Therefore, we aimed to evaluate if the source of dietary P rather than the total amount of P ingested determines total phosphaturia and it was accessed to what extent inorganic P intake modifies phosphaturia Method A 3-day dietary survey was performed in 71 stages G2-3 CKD patients with metabolic syndrome to estimate the amount and source of P in the diet. Blood and 24-hour urine-samples were collected. Total phosphaturia, fractional excretion of P (FeP%), urinary P/eGFR ratio (mg/day/GFR that reflects the urine P excretion relative to renal function), P/creatinine ratio, urinary urea /Cr ratio, and urinary P/urea ratio (that reflects daily intestinal absorption of P relative to the amount of proteins absorbed and metabolized) were evaluated. P/urea ratio was categorized into tertiles and contrasted in terms of the other variables analyzed (T1=<0.027 mg/mg, T2=0.027-0.033 mg/mg, T3= >0.033 mg/mg). Statistics were performed using R 3.6.2, RStudio, Tidyverse, and tableone v0.10.0 packages. Results Patients` age was 61±9 years, and eGFR was 68±21 ml/min/1.73m2. Estimated P intake was 869±289 mg/day. According to sources, P intake was 64% from animal sources, 22% from vegetable sources, and 14% from inorganic P. Total P intake did not correlate with urinary P (r=0.18, p=0.12), urinary P/eGFR (r=-0.32, p=0.79), or FeP (r=-0.08, p=0.48). Figure 1 shows that patients ingesting more P have a greater intake of inorganic P. There was a correlation between P intake and P/Urea ratio (p=0.008). Patients in the upper urinary P/urea tertile showed the highest daily P intake (p=0.04), and inorganic P (p=0.03). These patients from tertile 3 also showed the highest amount of urinary P excretion (p=0.04). Conclusion Urinary P/urea reflects the total P intake and, more importantly, provides information about the amount of inorganic P. Therefore, the P/urea ratio may be used to guide the appropriate nutritional advice for CKD patients.