Stremke ER, et al. - Researchers performed a secondary analysis from 2-week balance studies with tightly controlled phosphorus and calcium intakes, to investigate if 24-hour urine phosphorus is reliable and accurate as a biomarker of phosphorus intake and absorption in moderate CKD. They used a published equation to assess the accuracy of 24-hour urine phosphorus to predict phosphorus intake. They also evaluated the associations of 24-hour urine phosphorus with phosphorus intake, net absorption, and retention. They found high variability of 24-hour urine phosphorus in a sample of eight patients with moderate CKD on a tightly controlled dietary intake. Findings demonstrated no association of 24-hour urine phosphorus with dietary phosphorus intake or absorption. Rather, an inverse association of it with phosphorus retention was shown.