title: Estimation of 24-hour sodium excretion from spot urine samples.
abstract: Despite the effects of sodium intake on blood pressure and on response to antihypertensive medication, sodium intake is rarely monitored in clinical practice. The current method, the 24-hour urine collection for sodium excretion, is cumbersome, often incorrectly performed, and not commonly ordered. Further, its results have limited meaning because of the substantial day-to-day variation in sodium intake. A spot urine test to enable convenient, inexpensive, and serial monitoring of sodium excretion would be desirable. In this study, the accuracy of predicting 24-hour sodium excretion from a spot urine sample was assessed. The urine sodium/creatinine ratio was determined from the following urine samples: an "AM sample," submitted at the beginning of the 24-hour urine collection; a "PM sample" collected in the later afternoon/early evening before dinner, at roughly the midpoint of the collection; and a "random sample," collected after its completion. The ratio was then corrected for 24-hour creatinine excretion. The strongest correlation between predicted and actual 24-hour sodium excretion was observed with the PM sample collected near the midpoint (r=0.86, P<.001). This sample also identified persons with sodium excretion <100 mEq/d with a sensitivity of 100% and specificity of 82%. The sodium/creatinine ratio from a spot urine sample collected in the late afternoon/early evening at roughly the midpoint of the 24-hour collection, and adjusted for 24-hour creatinine excretion, strongly correlated with 24-hour sodium excretion. Additional studies are merited to further evaluate the role of the spot urine sample in assessing sodium intake.
authors.affiliation: Department of Medicine, Division of Nephrology and Hypertension, New York Presbyterian Hospital, Weill Cornell Medical Center, New York, NY, USA. sjmann@med.cornell.edu
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Mann
authors.forename: Linda M
authors.initials: LM
authors.lastname: Gerber
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002940:Circadian Rhythm / Q000502:physiology*; D003404:Creatinine / Q000652:urine; D005260:Female; D006801:Humans; D006973:Hypertension / Q000652:urine*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012016:Reference Values; D012964:Sodium / Q000652:urine*; D017673:Sodium Chloride, Dietary / Q000008:administration & dosage; D055815:Young Adult
chemical_list: D017673:Sodium Chloride, Dietary; D012964:Sodium; D003404:Creatinine