Abstract P362: Validation of a Simple Method to Estimate Populational 24-h Urinary Sodium Excretion Based on a Casual Urine Specimen in an Adult Danish Population

Background: Tanaka et al (J Hum Hypert 2002; 16: 97-103) developed a simple method to estimate populational 24-h urinary sodium excretion using a casual urine specimen. However, this method was developed and validated in a Japanese population and thus this method might not be valid in populations that differ markedly from this population. Hypothesis: We assessed the hypothesis that the 24 hour urinary sodium excretion can be estimated from a casual spot urine using the Tanaka prediction method in a Danish general population. Methods: Overall 473 Danish individuals provided both a 24h urine collection and a spot urine sample. Data were collected in the Danthyr study (248 women aged 25-30 years and 60-65 years) and the Inter99 study (102 men and 113 women aged 30-60 years), respectively. Only participants with complete 24h urine collection (validated by the PABA method) were included. We compared the estimated daily sodium excretion through 24h urine (the gold standard) with the predicted 24 h sodium excretion from a causal urine specimen, using the Tanaka prediction method. Results: The predicted median 24 h sodium excretion (median [5 and 95 percentile]) was 8.6 gram [3.7;17.5] compared with a median measured 24 h sodium excretion of 8.9 [5.4; 13:1]. The mean (sd) residual (measured minus predicted 24 h sodium excretion) was 0.08 (3.7). The correlation (Spearman) between predicted and measured 24 h sodium excretion was 0.39 and the R 2 was 0.17. The proportion of individuals classified in the same or adjacent quintiles was 67%. Gross misclassification was found for 3% of the individuals. However, a Bland-Altman plot indicated a tendency of underestimation the sodium excretion for individuals with a high level of sodium excretion (>14 g per day). Conclusion: The Tanaka prediction model gives a reasonable estimate of sodium intake in a Danish population using casual spot urines. However, the validation study showed a tendency of underestimation of the sodium intake for individuals with a high sodium excretion (>14 g per day).