Variación de la fosfaturia en relación a la ingesta de fósforo

espanolObjetivo: La excrecion de fosfato en orina de 24-horas (24-h UPE) es considerado el gold-standard para valorar la ingesta de fosfato. El empleo de la ratio fosforo/creatinina (Pi/Cr) en primera orina de la manana como sustituto de la 24-h UPE es controvertido. El objetivo de este estudio es valorar la utilidad de la ratio Pi/Cr en muestras de orina de distintos periodos del dia en la estimacion de la 24-h UPE. Material y Metodos: Se realizo un estudio transversal sobre 21 sujetos sanos con funcion renal normal. Los sujetos realizaron un registro dietetico durante tres dias. El tercer dia recogieron de forma fraccionada la orina de 24-horas. Ademas, se analizaron muestras sanguineas. Se emplearon correlaciones de Spearman y el metodo de Bland-Altman para valorar la concordancia entre los distintos metodos de medir la excrecion urinaria de fosfato. Resultados: La ingesta, la 24-h UPE y la ratio Pi/Cr variaron durante el dia (p Conclusiones: No observamos correlacion entre la ingesta de fosfato y su excrecion urinaria. La ratio Pi/ Cr recogida en primera orina de la manana o durante la noche podrian sustituir a la recogida de orina de 24-horas en la estimacion de la 24-h UPE. EnglishBackground: 24-hour urinary phosphate excretion (24-h UPE) is considered by many the gold-standard method to assess phosphate intake. Although phosphorus to creatinine ratio (Pi/Cr) has been proposed as surrogate of 24-h UPE, further validation is required. Thus, this study aims to evaluate the usefulness of Pi/Cr ratio at different day timing and spot urine samples throughout the day in the estimation of 24-h UPE. Methods: We performed a cross-sectional study in 21 healthy individuals with normal renal function. They were prompted to record dietary intake during three days. On the third day, they collected 24-hour urine. Blood samples were drawn the day after completion of urine collection. Spearman’s correlation test and the Bland-Altman method were used to evaluate agreement between different methods. Results: Phosphate intake, 24-h UPE and Pi/Cr ratio widely varied throughout the day (p p=0.99). The lowest proportional dispersion observed using the Bland-Altman test were in the first morning urine void (-3.9%) and night urine spot (1.6%). Conclusion: The calculated phosphate intake and urinary phosphate excretion throughout the day are not correlated. Pi/Cr ratio in the first morning urine void and that collected during the night can be used interchangeably with 24-hour urine collection to estimate 24-h UPE.