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Revista médica de Chile

Print version ISSN 0034-9887


SEPULVEDA, Rodrigo A.; HUIDOBRO E., Juan Pablo; JARA, Aquiles  and  TAGLE, Rodrigo. A new equation to estimate daily natriuresis from parameters in plasma and spot urine sample in the Chilean population. Rev. méd. Chile [online]. 2021, vol.149, n.2, pp.178-186. ISSN 0034-9887.


Excessive sodium intake is associated with increased cardiovascular morbidity and mortality. Daily sodium intake is usually inferred from sodium excretion in a 24-hour urine collection, which is cumbersome and prone to errors. Different formulas have attempted to estimate 24-hour urinary sodium from a spot urine sample. Unfortunately, their concordances are insufficient and have not been tested in our population.


To develop an equation to predict 24-hour urine sodium from parameters in plasma and spot urine samples. To validate the equation and compare it with other formulas in Chilean population.

Material and Methods:

Analysis of 24-hour urine collections, plasma sample and spot urine sample from 174 adult outpatients (81% females) with an estimated glomerular filtration rate (eGFR) ≥ 60 mL/min/1.73m2. These were collected between 2015 and 2019 using standardized methods and educating patients about the correct method to collect 24 h urine samples. In all these patients, creatinine and electrolytes were measured in plasma and urine. A new equation was developed using a multiple linear regression model.


Twenty-four-hour urine sodium excretion was significantly correlated with age, weight, height, eGFR, plasma osmolarity, urine electrolytes and parameters obtained from spot urine sample, among others. The new equation had a linear correlation with 24-hour natriuresis of 0.91 and the concordance was 0.9. The predictive capacity of the new equation was better than the existing formulas.


We developed a formula to accurately predict daily natriuresis in the Chilean population.

Keywords : Diet Therapy; Hypertension; Natriuresis; Sodium Chloride; Urine Specimen Collection.

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