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.

Estudo de validação das equações de Tanaka e de Kawasaki para estimar a excreção diária de sódio através da coleta da urina casual

“…To overcome these issues, some protocols have been made, such as urine collection in shorter periods 8,10 and the estimation of sodium intake by measuring the sodium/creatinine ratio in casual urine 11,12 . For that, equations were developed to estimate the 24-hour sodium excretion, and, consequently, the salt consumption 4,[11][12][13] . The accuracy of such an estimation depends on a precisely measurement of the 24-hour creatinine excretion based on weight and height 11,12 .…”

Evaluation of using spot urine to replace 24 h urine sodium and potassium excretions

“…Studies have shown good correlations between Na:creatinine and K:creatinine in spot urine and respective ratios in 24 h urine (12,14,16) . In addition, Brown and colleagues showed that β coefficients derived from regression analyses of spot urine samples v. 24 h urinary Na excretions can be used to predict 24 h excretions with reasonable accuracy (15) .…”

“…Also, methods to predict 24 h Na and K excretions from spot urine have been evaluated (12)(13)(14)17) . Tanaka and colleagues developed a method to predict both 24 h Na and K excretions from a spot urine sample and a Danish method was developed to predict only Na excretion (12,13) .…”

Determinants and Changes Associated with Aldosterone Breakthrough after Angiotensin II Receptor Blockade in Patients with Type 2 Diabetes with Overt Nephropathy

“…Furthermore, we did not measure urine aldosterone and renin. Third, sodium intake was not assessed but indirectly evaluated with Mann's formula from spot UNaCR values as previously shown (18). Fourth, diuretic dosages were not reported during the study.…”

“…The 24-hour urinary sodium excretion, a good marker of daily sodium intake, was extrapolated from UNaCR in morning urine spots as previously shown using Mann's formula (18).…”