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Twenty‐Four‐Hour Urine Phosphorus is Highly Variable in Patients with Moderate Chronic Kidney Disease on a Controlled Phosphorus Intake
Author(s) -
Stremke Elizabeth R.,
McCabe Linda D.,
McCabe George P.,
Martin Berdine R.,
Wastney Meryl,
Moe Sharon M.,
Weaver Connie M.,
Peacock Munro,
Hill Gallant Kathleen M.
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.459.2
Subject(s) - phosphorus , urine , creatinine , renal function , kidney disease , excretion , intraclass correlation , zoology , chemistry , medicine , endocrinology , dietary reference intake , nutrient , biology , reproducibility , chromatography , organic chemistry
Twenty‐four‐hour urine phosphorus (24h uP) is commonly considered a good reflection of dietary phosphorus (P) intake in healthy adults in P balance because net absorption of P is linearly related to dietary intake over a wide range of intakes. This relationship has been assumed to also apply to patients with chronic kidney disease (CKD). However, factors other than dietary P intake and intestinal P absorption may affect 24h uP excretion, including the rate of net bone retention and soft tissue P deposition and retention. This study is a secondary analysis of the variation in 24‐hour urine phosphorus and its reliability as a measure of phosphorus intake in patients with moderate chronic kidney disease. Thirteen consecutive 24‐hour urines from 2‐week balance studies in 8 patients with estimated glomerular filtration rates 26–53 mL/min/1.73m 2 on a tightly‐controlled dietary phosphorus intake of 1564 ± 52 mg/d were analyzed for variability and reliability. Results show, while consuming a controlled P diet, there is wide day‐to‐day intrasubject (standard deviations from 105–208 mg/d or %CV 15–60) and intersubject variation in 24h uP (standard deviation of 267 mg/d or %CV =37), as well as phosphorus/creatinine ratio. Intraclass correlation coefficients were calculated for 24h uP (r = 0.65) and phosphorus/creatinine ratio (r = 0.60). From these values, it was estimated that the number of replicates needed to have at least 75% reliability for 24h uP or P/Cr is 2 (95% CI: 1,5), and more replicates if a greater degree of reliability is desired. While 75% is generally considered a threshold for an acceptable level of reliability, the 13 replicates that were available from these balance studies gave over 90% reliability in the measures of both 24h uP and P/Cr. Dietary phosphorus intake calculated from 24‐hour urine phosphorus underestimated intake in some patients by up to 98% and overestimated intake in others by up to 79%. In patients with moderate chronic kidney disease, 24h uP is highly variable and its use can lead to erroneous conclusions regarding dietary phosphorus intake. Support or Funding Information The parent study was a randomized controlled trial funded by Sanofi/Genzyme through an unrestricted investigator‐initiated grant to MP, and, in part, by a NCRR Clinical and Translational Sciences Award (U54‐RR025761, Shekhar, PI). This secondary analysis was supported through institutional funds of KMHG. KMHG is supported by NIH K01 DK102864.