Intended for healthcare professionals

Practice Practice Pointer

Hyponatraemia in primary care

BMJ 2019; 365 doi: (Published 09 May 2019) Cite this as: BMJ 2019;365:l1774
  1. Peter Jacob, specialist trainee in endocrinology and diabetes1,
  2. Claire Dow, consultant in older people’s services1,
  3. Shawarna S. Lasker, general practitioner2,
  4. William M. Drake, consultant endocrinologist1,
  5. Tahseen A. Chowdhury, consultant in diabetes1
  1. 1Barts Health NHS Trust, London, UK
  2. 2Kings Medical Centre, Essex, UK
  1. Correspondence to TA Chowdhury Tahseen.Chowdhury{at}

What you need to know

  • Mild hyponatraemia is associated with increased risk of falls and osteoporosis

  • Assessing volume status helps to guide differential diagnosis and options for management

  • Medications such as diuretics, antidepressants, antipsychotics, and anti-epileptics are common causes of hyponatraemia

  • Older people are particularly at risk of developing and suffering consequences of hyponatraemia

  • Check thyroid function and 9 am cortisol in all patients with hypovolaemic and euvolaemic hyponatraemia

Hyponatraemia is the most frequently observed electrolyte abnormality.1 Mild hyponatraemia is associated with cognitive deficits and falls, but in hospitalised patients it is associated with increased mortality.2 In primary care, patients are often found to have hyponatraemia during chronic disease monitoring. This prompts a focused re-evaluation to consider underlying causes such as medication, cancer, or adrenal insufficiency.23 In this article we provide a framework to assess patients with hyponatraemia in primary care.

Defining hyponatraemia

Hyponatraemia is defined as a serum sodium value below the reference range (lower limit is usually 133-135 mmol/L). Hyponatraemia is often subdivided into mild, moderate, severe, and life threatening, using a combination of the presence of associated symptoms and the sodium value.34 There is, however, a poor correlation between symptomatology and serum sodium level, so both must be taken into account when considering urgency of referral and subsequent management. Hyponatraemia may be acute (arbitrarily defined as an onset within 48 hours), chronic (>48 hours), or unknown (where management should be as per chronic).

Risks of mild hyponatraemia

Although it may appear to be asymptomatic, even at modest levels hyponatraemia may predispose to falls and cognitive deficits. In a case-control study of 122 patients with hyponatraemia and 244 matched controls, 21% of patients had been admitted with falls compared with 5% of controls.5 The risk of falls was elevated with any sodium value below 132 mmol/L. Chronic hyponatraemia is a risk factor …

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