Which investigations should be considered for a patient presenting with persistent fatigue after COVID-19?

For a patient presenting with persistent fatigue following COVID-19 infection, investigations should be considered primarily to exclude other diagnoses and identify any treatable conditions. These investigations include:

• Urinalysis for protein, blood, and glucose
• Full blood count
• Urea and electrolytes
• Liver function tests
• Thyroid function tests
• Erythrocyte sedimentation rate (ESR) or plasma viscosity
• C-reactive protein (CRP)
• Calcium and phosphate levels
• HbA1c
• Serum ferritin
• Coeliac disease screening
• Creatine kinase

Additional investigations may be considered based on clinical judgement, such as vitamin D, vitamin B12 and folate levels, serological tests if there is a history of infection, and 9am cortisol for adrenal insufficiency.

These investigations help to exclude other causes of fatigue and support the clinical diagnosis of conditions like myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS), which may be suspected if fatigue persists and is unexplained by other conditions.

Referral to specialist teams should be considered if diagnosis is uncertain or symptoms persist beyond 3 months.

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