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.
References: NICE NG206