To compare spot urine and 24 hour urine collection method in evaluating 24 hour sodium and potassium excretion in patients with hypertension.

From February 2017 to January 2018, 264 patients with hypertension in hypertension department of the First Affiliated Hospital of Xinjiang Medical University were enrolled in the study. 24 hour urine specimens and morning fasting spot urine specimens were collected for detecting urinary sodium, potassium and creatinine levels. The Tanaka, Kawasaki and INTERSALT formulas were used to estimate the 24 hour urinary sodium and potassium excretion. The paired rank sum test was used to compare the difference between the estimated value and the actual measured value. Spearman correlation was used to evaluate the relationship between the estimated value and the actual value of 24 h urinary sodium and potassium excretion.

The 24 hour urinary sodium value estimated by Tanaka formula (167.99 mmol/d) was higher than that estimated by actual 24 hour urinary sodium value (157.73 mmol/d), with no significant difference (Z=-0.23, P>0.05). The 24 hour urinary sodium value estimated by Kawasaki formula (217.66 mmol/d) was also higher than that estimated by actual 24 hour urinary sodium value, with significant difference (t=-8.81, P<0.05). The 24 hour urinary sodium value estimated by INTERSALT formula (154.71 mmol/d) was lower than the actual 24 hour urinary sodium value, and the difference was statistically significant (Z=-3.53, P<0.01). The correlation coefficients between the estimated values of Tanaka, Kawasaki and INTERSALT formulas and the actual 24 h urine sodium value were 0.68, 0.55, 0.58, respectively, (all P<0.01). Tanaka formula estimated potassium excretion value (39.51 mmol/d) was lower than the actual measured value (42.90 mmol/d), the difference was statistically significant (Z=-3.47, P<0.05), the correlation coefficient was 0.50, (P<0.01).

In hypertensive patients, the 24 h urinary sodium excretion and urinary potassium estimated by formulas is underestimated or overestimated in varying degrees, and the correlation is low. There are some inaccuracies and limitations in estimating the 24 h urinary sodium and potassium excretion levels of hypertensive patients by spot urine method.