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What initial tests should be performed in primary care to determine whether

Guideline-aligned answer with reasoning, red flags and references. Clinically reviewed by Dr Kola Tytler MBBS CertHE MBA MSt MRCGP.

Posted: 5 August 2026Updated: 5 August 2026 Guideline-Aligned (High Confidence) Clinically Reviewed

Initial primary-care work-up

  • Repeat serum potassium at an interval guided by clinical judgement to exclude a spurious result and identify a rapidly falling concentration.
  • Request urea and electrolytes including potassium, sodium and chloride, plus magnesium, glucose, creatinine and bicarbonate.
  • Obtain an ECG as appropriate to identify hypokalaemia-associated ECG abnormalities or arrhythmia.
  • Take a targeted history, including vomiting or diarrhoea, medication and treatment use, alcohol and liquorice intake, diet, comorbidity, family history, polydipsia and nocturnal polyuria.
  • Examine blood pressure and volume status, and look for dehydration, malnutrition, abdominal signs, muscle weakness and signs of thyrotoxicosis.

To distinguish the likely mechanism when the cause is not apparent

  • Measure urinary potassium, chloride, creatinine and sodium; these urinary electrolytes may help differentiate renal from non-renal causes, supporting distinction between renal potassium loss and gastrointestinal potassium loss.
  • Use bicarbonate and, where needed, venous blood gas to assess for acid–base disturbance, because metabolic alkalosis is a recognised context for hypokalaemia.
  • Check magnesium because hypomagnesaemia can coexist and potassium may be difficult to correct until magnesium is corrected.
  • Check glucose and review exposure to insulin and beta-agonists, as increased insulin activity and beta-adrenergic activity are recognised causes of transcellular potassium shift.
  • Request thyroid-stimulating hormone if thyrotoxic periodic paralysis is a possibility.
  • Request aldosterone and renin when an endocrine or specific renal potassium-wasting disorder is suspected.
  • Consider calcium and/or phosphorus to exclude associated electrolyte abnormalities, and measure digoxin concentration where relevant.

Escalate rather than complete a routine outpatient work-up for potassium below 2.5 mmol/L, hypokalaemic symptoms, or clinical signs of hypovolaemia, thyrotoxic crisis, significant acid–base disturbance, hyperosmolar hyperglycaemic state or diabetic ketoacidosis.

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