Can methods based on spot urine samples be used to estimate average population 24 h sodium excretion? Results from the Isfahan Salt Study

• Published in: Public health nutrition Vol. 23; no. 2; pp. 202 - 213
• Main Authors: Mohammadifard, Noushin, Marateb, Hamidreza, Mansourian, Marjan, Khosravi, Alireza, Abdollahi, Zahra, Campbell, Norman Rc, Webster, Jacqui, Petersen, Kristina, Sarrafzadegan, Nizal
• Format: Journal Article
• Language: English
• Published: England Cambridge University Press 01.02.2020
• Subjects: Adult; Adults; Assessment and Methodology; Bias; Biomarkers - urine; Diet; Diet Surveys; Fasting; Feeding Behavior; Female; Formulas (mathematics); Humans; Iran; Laboratories; Male; Mathematical analysis; Medical personnel; Methods; Middle Aged; Neural networks; Population; Population characteristics; Research centers; Research Paper; Salt; Salts; Sodium; Sodium - urine; Sodium, Dietary - administration & dosage; Sodium, Dietary - urine; Studies; Urinalysis - methods; Urinalysis - standards; Urine; Urine Specimen Collection - methods; Urine Specimen Collection - standards; Iran; Urine; Validation; Salt; Spot urine; Diet; Sodium; 24 h Urine collection
• ISSN: 1368-9800; 1475-2727
• DOI: 10.1017/S136898001900257X

To assess agreement between established methods of estimating salt intake from spot urine collections and 24 h urinary Na (24hUNa) and then to develop a valid formula that can be used in the Iranian population to estimate salt intake from spot urine samples. A validation study. Three spot urine samples were collected (fasting second-void morning; afternoon; evening) on the same day as a 24 h urine collection. We estimated 24hUNa from spot specimens using the Kawasaki, Tanaka and INTERSALT equations. Two new formulas were developed, the Iran formula 1 (Iran 1) and Iran formula 2 (Iran 2), based on our population characteristics. Iranian adults recruited in 2014-2015. Healthy volunteer adults aged ≥18 years. With all three spot urine specimens, predicted population 24hUNa was underestimated based on the INTERSALT equation (-469 to -708 mg/d; all P < 0·05) and conversely overestimation occurred with the Kawasaki equation (926 to 1080 mg/d; all P < 0·01). The Tanaka equation produced comparable estimates to measured 24hUNa (-151 to 86 mg/d; all P > 0·49). The newly derived formulas, Iran 1 and Iran 2, showed less mean bias than the established equations (Iran 1: 43 to 80 mg/d, all P > 0·55; Iran 2: 22 to 90 mg/d, all P > 0·50). In this Iranian sample, the Tanaka equation and newly derived formulas produced group-level estimates comparable to measured 24hUNa. The newly developed formulas showed less mean bias than established equations; however, they need to be tested for generalization in a larger sample.