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Collaboration Centre Centre of Excellence Comparisons of spot vs 24-h urine samples for estimating salt intake Chen Ji a, Michelle A Miller a, Antonella.

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Presentation on theme: "Collaboration Centre Centre of Excellence Comparisons of spot vs 24-h urine samples for estimating salt intake Chen Ji a, Michelle A Miller a, Antonella."— Presentation transcript:

1 Collaboration Centre Centre of Excellence Comparisons of spot vs 24-h urine samples for estimating salt intake Chen Ji a, Michelle A Miller a, Antonella Venezia b, Pasquale Strazzullo b, and Francesco P Cappuccio a a University of Warwick, W.H.O Collaborating Centre for Nutrition, Coventry, UK b Department of Clinical & Experimental Medicine, Federico II University of Naples, Italy

2 Collaboration Centre Centre of Excellence Background In steady state, most of Na eaten in a day is excreted through urine in the following 24-h 24-h urinary Na excretion ‘gold standard’ for measuring sodium (salt) intake both in individuals and in populations In large population studies 24-h collections often deemed inconvenient, hence alternative methods suggested (e.g. spot and timed urines) Their reliability and reproducibility often disappointing

3 Collaboration Centre Centre of Excellence Aim To assess reliability and reproducibility of estimations of 24-h urinary Na excretion through timed spot urines compared to 24-h Na output in two independent population samples including men and women from different ethnic groups

4 Collaboration Centre Centre of Excellence Data Study 1: Discovery sample 915 British men & women aged (297 W, 326 B, 292 SA) Study 1: Discovery sample 915 British men & women aged (297 W, 326 B, 292 SA) Study 2: Validation sample 148 Italian White men aged Study 2: Validation sample 148 Italian White men aged Na, Cr in “independent” 24-h and timed spot urines Reliability and Reproducibility Tanaka’s method † Arithmetic extrapolation method Reliability and Reproducibility Tanaka’s method † Arithmetic extrapolation method †: Tanaka T et al. J Hum Hyper,2002;16,

5 Collaboration Centre Centre of Excellence Methods Tanaka’s method 24-h Ur Cr≈Predicted 24-h Ur Cr 24-h Ur Na/Cr  timed Ur Na/Cr 24-h Ur Na  timed Ur Na/Cr  Predicted 24-h Ur Cr 24-h Ur Na = timed Ur Na  timed Ur Vol  (24- h/timed Ur collection time) Predicted 24-h Ur Cr ~ Age, Height, Weight Arithmetic extrapolation method

6 Collaboration Centre Centre of Excellence Methods Tanaka’s method o Spearman’s rank Correlation and Quintile positions comparison o Bland-Altman plot  Graphical comparison o Receiver Operating Characteristic curve & Sensitivity/Specificity  >100 mmol/day as positive Arithmetic extrapolation method

7 Collaboration Centre Centre of Excellence Results Discovery sample – Correlation by Tanaka’s and Arithmetic methods Spearman's rankWhiteAfrican originSouth Asian Female0.330 (<0.001)0.055 (=0.436)0.310 (<0.001) Male0.251 (=0.004)0.166 (=0.065)0.187 (=0.020) Spearman's rankWhiteAfrican originSouth Asian Female0.367 (<0.001)0.116 (=0.102)0.264 (=0.002) Male0.282 (=0.001)0.221 (=0.013)0.170 (=0.035) Tanaka’s method vs Measured 24-h urinary sodium Arithmetic method vs Measured 24-h urinary sodium

8 Collaboration Centre Centre of Excellence Results Discovery sample – Quintile positions by Tanaka’s and Arithmetic methods Tanaka’s method Arithmetic method urinary sodium (mmol/24h)

9 Collaboration Centre Centre of Excellence Average of estimated and measured 24-h urinary sodium Results Discovery sample – Bland-Altman plot by Tanaka’s method Female Male Estimated - Measured 95% CI Mean diff Overestimation Underestimation

10 Collaboration Centre Centre of Excellence Results Discovery sample – Bland-Altman plot by Arithmetic method log(estimated) - log(measured) Average of log (estimated) and log(measured) urinary sodium Female Male

11 Collaboration Centre Centre of Excellence Results Discovery sample – ROC, sensitivity/specificity by Tanaka’s method Note: Measured 24-h urinary sodium > 100 mmol/day is defined as positive AUC=0.631 Sensitivity=95.3% Specificity=6.3% AUC=0.550 Sensitivity=100% Specificity=0% AUC=0.652 Sensitivity=95.8% Specificity=8.5% AUC=0.582 Sensitivity=100% Specificity=0% AUC=0.521 Sensitivity=100% Specificity=0% AUC=0.538 Sensitivity=100% Specificity=0% Sensitivity Female Male 1-specificity WhiteAfrican originSouth Asian

12 Collaboration Centre Centre of Excellence Results Validation sample – Correlation & Quintile positions Tanaka’s method Arithmetic method Spearman's rank Measured 24-h urinary sodium Tanaka’s method0.499 (<0.001) Arithmetic method0.329(<0.001)

13 Collaboration Centre Centre of Excellence Results Validation sample – Bland-Altman plot & ROC, Sensitivity/specificity Note: Measured 24-h urinary sodium > 100 mmol/day is defined as positive AUC=0.649 Sensitivity=100% Specificity=0% AUC=0.576 Sensitivity=85.5% Specificity=20.0% ROC Curve 1-Specificity Sensitivity Average of methods Tanaka’s method Arithmetic method Estimated - Measured Log(estimated/me asured)

14 Collaboration Centre Centre of Excellence Spot timed urinary Na does not provide reliable and reproducible estimates of 24-h urinary Na excretion 24-h urinary collection for the measurement of urinary Na excretion remains the preferred tool for assessing salt intake Conclusions

15 Collaboration Centre Centre of Excellence Thank you


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