title: Reliable Quantification of the Potential for Equations Based on Spot Urine Samples to Estimate Population Salt Intake: Protocol for a Systematic Review and Meta-Analysis.
abstract: BACKGROUND
  Methods based on spot urine samples (a single sample at one time-point) have been identified as a possible alternative approach to 24-hour urine samples for determining mean population salt intake.
  
  
  OBJECTIVE
  The aim of this study is to identify a reliable method for estimating mean population salt intake from spot urine samples. This will be done by comparing the performance of existing equations against one other and against estimates derived from 24-hour urine samples. The effects of factors such as ethnicity, sex, age, body mass index, antihypertensive drug use, health status, and timing of spot urine collection will be explored. The capacity of spot urine samples to measure change in salt intake over time will also be determined. Finally, we aim to develop a novel equation (or equations) that performs better than existing equations to estimate mean population salt intake.
  
  
  METHODS
  A systematic review and meta-analysis of individual participant data will be conducted. A search has been conducted to identify human studies that report salt (or sodium) excretion based upon 24-hour urine samples and spot urine samples. There were no restrictions on language, study sample size, or characteristics of the study population. MEDLINE via OvidSP (1946-present), Premedline via OvidSP, EMBASE, Global Health via OvidSP (1910-present), and the Cochrane Library were searched, and two reviewers identified eligible studies. The authors of these studies will be invited to contribute data according to a standard format. Individual participant records will be compiled and a series of analyses will be completed to: (1) compare existing equations for estimating 24-hour salt intake from spot urine samples with 24-hour urine samples, and assess the degree of bias according to key demographic and clinical characteristics; (2) assess the reliability of using spot urine samples to measure population changes in salt intake overtime; and (3) develop a novel equation that performs better than existing equations to estimate mean population salt intake.
  
  
  RESULTS
  The search strategy identified 538 records; 100 records were obtained for review in full text and 73 have been confirmed as eligible. In addition, 68 abstracts were identified, some of which may contain data eligible for inclusion. Individual participant data will be requested from the authors of eligible studies.
  
  
  CONCLUSIONS
  Many equations for estimating salt intake from spot urine samples have been developed and validated, although most have been studied in very specific settings. This meta-analysis of individual participant data will enable a much broader understanding of the capacity for spot urine samples to estimate population salt intake.
authors.affiliation: The George Institute for Global Health, Peking University Health Science Center, Beijing, China.
authors.forename: Liping
authors.identifier: http://orcid.org/0000-0002-0945-8988
authors.initials: L
authors.lastname: Huang
authors.forename: Michelle
authors.identifier: http://orcid.org/0000-0003-2941-8147
authors.initials: M
authors.lastname: Crino
authors.forename: Jason Hy
authors.identifier: http://orcid.org/0000-0003-2073-3562
authors.initials: JH
authors.lastname: Wu
authors.forename: Mark
authors.identifier: http://orcid.org/0000-0001-9800-5296
authors.initials: M
authors.lastname: Woodward
authors.forename: Mary-Anne
authors.identifier: http://orcid.org/0000-0002-7807-2886
authors.initials: MA
authors.lastname: Land
authors.forename: Rachael
authors.identifier: http://orcid.org/0000-0002-0005-328X
authors.initials: R
authors.lastname: McLean
authors.forename: Jacqui
authors.identifier: http://orcid.org/0000-0003-3513-3340
authors.initials: J
authors.lastname: Webster
authors.forename: Batsaikhan
authors.identifier: http://orcid.org/0000-0001-8521-0303
authors.initials: B
authors.lastname: Enkhtungalag
authors.forename: Caryl A
authors.identifier: http://orcid.org/0000-0001-6586-7965
authors.initials: CA
authors.lastname: Nowson
authors.forename: Paul
authors.identifier: http://orcid.org/0000-0002-7511-5684
authors.initials: P
authors.lastname: Elliott
authors.forename: Mary
authors.identifier: http://orcid.org/0000-0001-6032-3774
authors.initials: M
authors.lastname: Cogswell
authors.forename: Ulla
authors.identifier: http://orcid.org/0000-0001-7770-8419
authors.initials: U
authors.lastname: Toft
authors.forename: Jose G
authors.identifier: http://orcid.org/0000-0002-0987-368X
authors.initials: JG
authors.lastname: Mill
authors.forename: Tania W
authors.identifier: http://orcid.org/0000-0002-8300-2073
authors.initials: TW
authors.lastname: Furlanetto
authors.forename: Jasminka Z
authors.identifier: http://orcid.org/0000-0002-2426-8584
authors.initials: JZ
authors.lastname: Ilich
authors.forename: Yet Hoi
authors.identifier: http://orcid.org/0000-0003-2739-580X
authors.initials: YH
authors.lastname: Hong
authors.forename: Damian
authors.identifier: http://orcid.org/0000-0002-2173-7322
authors.initials: D
authors.lastname: Cohall
authors.forename: Leonella
authors.identifier: http://orcid.org/0000-0002-9498-2214
authors.initials: L
authors.lastname: Luzardo
authors.forename: Oscar
authors.identifier: http://orcid.org/0000-0002-0975-9924
authors.initials: O
authors.lastname: Noboa
authors.forename: Ellen
authors.identifier: http://orcid.org/0000-0002-7600-6025
authors.initials: E
authors.lastname: Holm
authors.forename: Alexander L
authors.identifier: http://orcid.org/0000-0003-0440-7417
authors.initials: AL
authors.lastname: Gerbes
authors.forename: Bahaa
authors.identifier: http://orcid.org/0000-0001-9583-8508
authors.initials: B
authors.lastname: Senousy
authors.forename: Sonat
authors.identifier: http://orcid.org/0000-0002-8018-4879
authors.initials: S
authors.lastname: Pinar Kara
authors.forename: Lizzy M
authors.identifier: http://orcid.org/0000-0002-7434-0038
authors.initials: LM
authors.lastname: Brewster
authors.forename: Hirotsugu
authors.identifier: http://orcid.org/0000-0002-7742-4253
authors.initials: H
authors.lastname: Ueshima
authors.forename: Srinivas
authors.identifier: http://orcid.org/0000-0002-2855-0819
authors.initials: S
authors.lastname: Subramanian
authors.forename: Boon Wee
authors.identifier: http://orcid.org/0000-0002-4911-8507
authors.initials: BW
authors.lastname: Teo
authors.forename: Norrina
authors.identifier: http://orcid.org/0000-0002-6993-4384
authors.initials: N
authors.lastname: Allen
authors.forename: Sohel Reza
authors.identifier: http://orcid.org/0000-0002-7498-4634
authors.initials: SR
authors.lastname: Choudhury
authors.forename: Jorge
authors.identifier: http://orcid.org/0000-0002-0133-7217
authors.initials: J
authors.lastname: Polonia
authors.forename: Yoshinari
authors.identifier: http://orcid.org/0000-0002-7448-3397
authors.initials: Y
authors.lastname: Yasuda
authors.forename: Norm Rc
authors.identifier: http://orcid.org/0000-0002-1093-4742
authors.initials: NR
authors.lastname: Campbell
authors.forename: Bruce
authors.identifier: http://orcid.org/0000-0002-0490-7465
authors.initials: B
authors.lastname: Neal
authors.forename: Kristina S
authors.identifier: http://orcid.org/0000-0003-3914-0353
authors.initials: KS
authors.lastname: Petersen
keywords: 24-hour urine collection; dietary salt; meta-analysis; sodium; spot urine collection; systematic review