Using Spot Urine Sodiums

A recent study (AKN Pedersen et al. JPEN shows the utility of obtaining urine spot sodiums in patients with an ileostomy. Thanks to Kipp Ellsworth for sharing this reference.

Full link: A Single Urine Sodium Measurement May Validly Estimate 24‐hour Urine Sodium Excretion in Patients With an Ileostomy

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.

Design: In this prospective, observational study, we included 16 adult individuals: 8 stable patients with an ileostomy and 8 healthy volunteers with intact intestines

Key finding:

  • 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.

My take: In patients with ileostomy (and also short bowel syndrome), periodic urine sodium values (from morning or mid-day) will help detect subclinical sodium depletion.

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Understanding Sodium Intake and Cardiovascular Risk

A recent review (ME Cogswell et al. NEJM 2016; 375: 580-5) helps sort out some of the confusion regarding sodium intake and cardiovascular disease. In brief, the authors point out the excessive sodium intake is clearly linked to heart disease, stroke and death.  The importance has been questioned by some due to a few studies suggesting that low sodium intake could also increase the risk of cardiovascular disease.

The authors note that these studies have shown only weak associations & were likely a matter of reverse causation due to the low sodium group having increased numbers of participants with numerous health issues (eg diabetes, hypertension, chronic illness and cardiovascular disease).

By looking at these results based on “Hill’s Criteria” to assess whether an association is causal, the authors show that the association of low sodium intake and cardiovascular disease indicates that this association is NOT causal.

Hill’s criteria:

  • Strength -degree which the exposure is associated with the outcome
  • Consistency -is this finding observed by different persons, in different places/times
  • Specificity -is observation limited to the exposure and the outcome
  • Temporality -did observation cause the outcome or did the outcome affect changes that lead to observation
  • Biologic gradient -?dose-response noted
  • Plausibility -is there a physiologic basis
  • Coherence -does this association conflict with other known facts
  • Experiment -is the finding affected by actions to prevent the exposure
  • Analogy -does an exposure with a similar physiologic action cause the outcome

The authors note that population exposure to sodium correlates better than individual exposure, perhaps due to measurement issues. Key points:

  • “There is strong evidence of a linear, dose-response effect of sodium reduction on blood pressure.  In addition, the evidence shows that sodium reduction prevents cardiovascular disease.”
  • “Reducing the average sodium intake by just 400 mg per day could potentially avert as many as 28,000 deaths and save $7 billion in health care costs annually in the United States.”
  • “Yet sodium levels are high before food reaches the kitchen or table, and the sodium density of the U.S. diet has changed little despite consumer education encouraging individual behavior change.”

My take: If we are to take advantage of the science to reduce cardiovascular deaths, we need to convince manufacturers and restaurants to reduce sodium.

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