Usefulness of urinary parameters in advanced chronic kidney disease

Abstract

This review discusses the diagnostic value of urinary parameters in the setting of advanced chronic kidney disease and we present the key concepts that summarize the suggestions of the manuscript. Urinary volumeThe amount of fluid intake may be a non-established risk factor for CKD. For these patients, a urinary output ≥2–3l/day is a reasonable proposal. This recommendation is not applicable to patients with cardiorenal syndrome or fluid overload risk. NaurThis determination is very useful to monitor salt intake. Reducing urinary Na<120mEquiv./day (≅salt intake≤5–6g) is a reasonable objective. Urinary urea nitrogen (UUN)This parameter is useful to estimate protein intake (Maroni BJ equation). A protein intake between 48–72g (0.8–0.9g/kg/day according to weight) is equivalent to UUN 7–10g/day approximately. Acid load and potassiumAcid load reduction may be an additional strategy in the nutritional management of this population. It may be estimated indirectly from a diet survey or by measuring the elimination of UUN and Kur. The limits of this recommendation have not been established, but we propose a cautious and prudent diet of fruit and vegetables. PhosphorusThere is a significant positive correlation between phosphorus and protein, both in dietary records and urine elimination. Based on this information, we suggest a urinary P excretion<800mg/day or<600mg/day for patients with GFR<25ml/min or <15ml/min, respectively. ConclusionUrinary parameters provide sensitive and useful knowledge for clinical practice, provide information about the dietary habits of patients and the adherence to our recommendations.