Twenty-Four-Hour Urine Phosphorus as a Biomarker of Dietary Phosphorus Intake and Absorption in CKD: A Secondary Analysis from a Controlled Diet Balance Study

Elizabeth R Stremke, Linda D McCabe, George P McCabe, Berdine R Martin, Sharon M Moe, Connie M Weaver, Munro Peacock, Kathleen M Hill Gallant

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


BACKGROUND AND OBJECTIVES: Twenty-four-hour urine phosphorus is commonly used as a surrogate measure for phosphorus intake and absorption in research studies, but its reliability and accuracy are unproven in health or CKD. This secondary analysis sought to determine the reliability and accuracy of 24-hour urine phosphorus as a biomarker of phosphorus intake and absorption in moderate CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Eight patients with stage 3-4 CKD participated in 2-week balance studies with tightly controlled phosphorus and calcium intakes. Thirteen 24-hour urine collections per patient were analyzed for variability and reliability of 24-hour urine phosphorus and phosphorus-to-creatinine ratio. The accuracy of 24-hour urine phosphorus to predict phosphorus intake was determined using a published equation. The relationships of 24-hour urine phosphorus with phosphorus intake, net absorption, and retention were determined.

RESULTS: There was wide day-to-day variation in 24-hour urine phosphorus within and among subjects (coefficient of variation of 30% and 37%, respectively). Two 24-hour urine measures were needed to achieve ≥75% reliability. Estimating dietary phosphorus intake from a single 24-hour urine resulted in underestimation up to 98% in some patients and overestimation up to 79% in others. Twenty-four-hour urine phosphorus negatively correlated with whole-body retention but was not related to net absorption.

CONCLUSIONS: From a sample of eight patients with moderate CKD on a tightly controlled dietary intake, 24-hour urine phosphorus was highly variable and did not relate to dietary phosphorus intake or absorption, rather it inversely related to phosphorus retention.

Original languageEnglish (US)
Pages (from-to)1002-1012
Number of pages11
JournalClinical journal of the American Society of Nephrology : CJASN
Issue number7
StatePublished - Jul 6 2018

Bibliographical note

Copyright © 2018 by the American Society of Nephrology.


  • Biomarkers/urine
  • Diet Therapy
  • Female
  • Humans
  • Male
  • Middle Aged
  • Monitoring, Physiologic
  • Phosphorus/urine
  • Phosphorus, Dietary/administration & dosage
  • Renal Insufficiency, Chronic/metabolism

PubMed: MeSH publication types

  • Journal Article
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't


Dive into the research topics of 'Twenty-Four-Hour Urine Phosphorus as a Biomarker of Dietary Phosphorus Intake and Absorption in CKD: A Secondary Analysis from a Controlled Diet Balance Study'. Together they form a unique fingerprint.

Cite this