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Abstract: PO1500

Accurate Estimation of Individual Sodium Intake with Repeated Spot Urine Sampling

Session Information

Category: Fluid, Electrolyte, and Acid-Base Disorders

  • 902 Fluid, Electrolyte, and Acid-Base Disorders: Clinical

Authors

  • Ginos, Bigina NR, Amsterdam University Medical Centres, location Academic Medical Centre, University of Amsterdam, Amsterdam, Netherlands
  • Vogt, Liffert, Amsterdam University Medical Centres, location Academic Medical Centre, University of Amsterdam, Amsterdam, Netherlands
  • Frings-Meuthen, Petra, German Aerospace Center (DLR), Institute of Aerospace Medicine, Cologne, Germany
  • Heer, Martina D., Institute of Nutritional and Food Sciences, University of Bonn, Bonn, Germany
  • Olde Engberink, Rik Hg, Amsterdam University Medical Centres, location Academic Medical Centre, University of Amsterdam, Amsterdam, Netherlands
Background

In clinical practice, individual sodium (Na+) intake is estimated by measuring Na+ excretion in one 24-h urine collection (UC), whereas long-term Na+ balance studies indicate that 7 consecutive 24-h UCs may be needed. To reduce the burden of 24-h UC, single spot urine based alternatives have been suggested, but this approach has been shown to be very inaccurate. Whether the use of repeated spot UCs is an appropriate alternative for (multiple) 24-h UCs to estimate Na+ intake is unknown.

Methods

We performed a post-hoc analysis of a metabolic ward study in 8 healthy male adults who consumed a 7-d diet with a fixed amount of 200 mmol/d Na+. Urine was collected in 4 daily intervals (7-13h, 13-19h, 19-23h and 23-7h). After reaching steady state, we estimated Na+ intake by single and repeated 24-h UCs and repeated spot UCs, using the Kawasaki formula with measured 24-h urine creatinine excretion.

Results

After day 5, mean 24-h Na+ excretion matched intake, indicating that steady state was achieved (Fig 1A). Mean absolute differences (Δ) between measured Na+ intake and 3-d spot UC estimates were 18.8 (SD 14.6), 32.3 (SD 18.7), 74.6 (SD 30.0) and 28.2 (SD 19.8) mmol for interval 7-13h, 13-19h, 19-23h and 23-7h, respectively (Fig 1B). With the exception of samples collected between 19-23h, Na+ intake estimates by 3-d spot UCs did not significantly differ from Na+ intake estimates by single (Δ 29.8 mmol; SD 23.9) and three 24-h UCs (Δ 22.9 mmol; SD 11.4).

Conclusion

Bias in Na+ intake estimation did not significantly differ between repeated spot UCs and single and repeated 24-h UCs. Adequately powered studies need to confirm whether repeated spot UCs are an accurate and low burden alternative to 24-h UCs.

Figure 1. (A) Mean 24-h Na+ excretion during 7-d diet. (B) Comparison of the performance of three consecutive spot UCs (blue), single 24-h UC (green) and three consecutive 24-h UCs (red) for estimating Na+ intake (200 mmol/d). Absolute differences between estimated and measured Na+ intake. Data are mean and SD.

Funding

  • Private Foundation Support