A Single Urine Sodium Measurement May Validly Estimate 24-hour Urine Sodium Excretion in Patients With an Ileostomy

Abstract

Background: Sodium deficiency in patients with an ileostomy is associated with chronic dehydration and may be difficult to detect. We aimed to investigate if the sodium concentration in a single spot urine sample may be used as a proxy for 24-hour urine sodium excretion.

Methods: In a prospective observational study with 8 patients with an ileostomy and 8 volunteers with intact intestines, we investigated the correlations and agreements between spot urine sodium concentrations and 24-hour urine sodium excretions. Spot urine samples were drawn from every micturition during 24 hours, and relevant blood samples were drawn. All participants documented their food and fluid intakes.

Results: There was a high and statistically significant correlation between 24-hour natriuresis and urine sodium concentrations in both morning spot samples (n = 8, Spearman's rho [ρ] = 0.78, P = 0.03) and midday spot samples (n = 8, ρ = 0.82, P = 0.02) in the patients with an ileostomy. The agreement between methods was fair (bias = -1.5, limits of agreement = -32.3 to 29.4). There were no statistically significant associations for evening samples or for samples from volunteers with intact intestines independently of time of day.

Conclusion: A single spot urine sodium sample obtained in the morning or midday may estimate 24-hour urine sodium excretion in patients with an ileostomy and thus help to identify sodium depletion.

Keywords: dehydration; ileostomy; natriuresis; short bowel syndrome; water-electrolyte balance.

Figure 1

Intake of fluid (A) and sodium (B) were similar between groups, but patients with an ileostomy had statistically significantly lower urine volume (C) and natriuresis (D) than healthy volunteers with intact intestines (Mann‐Whitney tests, n = 8 in each group).

Figure 2

Morning and midday spot urine samples were highly correlated with 24‐hour natriuresis for patients with an ileostomy (A), whereas no associations were observed for the healthy volunteers with intact intestines (B) (Spearman's rho [ρ], n = 8). Bland‐Altman plots of 24‐hour natriuresis and morning spot samples showed good agreement between methods for ileostomates (B) but not for healthy volunteers (C). Each participants’ 24‐hour natriuresis is presented (E and F) with indications of normal range (114–210 mmol/d) and minimum reference range (50 mmol/d).

Figure 3

The individual variation of sodium concentration in spot urine samples was lower in patients with an ileostomy (A) than in healthy volunteers with intact intestines (B) (Mann‐Whitney test). Spot samples were collected from every micturition during 24 hours for each participant, and 41% of the samples were ≤20 mmol/L among ileostomates, whereas 4% of the samples from healthy volunteers were ≤20 mmol/L.

Figure 4

No association between sodium intake and natriuresis for patients with an ileostomy (n = 8) were identified (A), whereas this correlation was strong for the healthy volunteers with intact intestines (B) (Spearman's rho [ρ], n = 8).

Figure 5

For patients with an ileostomy, there was a strong and statistically significant inverse correlation between intake of hypo‐osmolar fluids and natriuresis and a tendency to a positive association between intake of iso‐osmolar fluids (Spearman's rho [ρ], n = 8).