Feeling tired for a few days is common. When tiredness persists, worsens or has no clear explanation, I look at physical, psychological, lifestyle and medication-related causes before choosing tests that fit the clinical picture.
In a private GP consultation, I review the pattern of fatigue, sleep, mood, diet, medicines, menstrual history, infections and accompanying symptoms before recommending investigations.
Blood tests can identify some treatable contributors, but normal results also guide the next clinical question. They do not automatically prove that nothing is wrong.
Written & reviewed by
Dr George XynopoulosConsultant Physician & Cardiologist · GMC 3502763 · Reviewed by Dr George Xynopoulos, GMC 3502763
Clinical review date: 21 August 2026
View full profileCommon causes of persistent tiredness
Fatigue is a symptom, not a diagnosis. It may be linked to poor sleep, stress, low mood, anaemia, thyroid disease, diabetes, nutritional deficiency, infection, medication effects or other medical conditions.
| Pattern or accompanying symptom | Possible clinical direction | Typical next step |
|---|---|---|
| Breathlessness, paleness or heavy periods | Anaemia or iron deficiency | GP assessment and targeted blood tests |
| Weight change, heat/cold intolerance | Thyroid or metabolic cause | Clinical review with thyroid/metabolic testing where indicated |
| Thirst and frequent urination | Diabetes or other metabolic issue | Prompt GP review and glucose/HbA1c assessment |
| Snoring or unrefreshing sleep | Sleep disorder | Sleep history and appropriate referral pathway |
When blood tests may be useful
Depending on your history, a clinician may consider a full blood count, ferritin, thyroid function, glucose or HbA1c, kidney and liver markers, vitamin B12, folate or vitamin D. The right panel depends on your symptoms and risk factors.
When to seek urgent help
Urgent assessment is important if fatigue comes with chest pain, severe breathlessness, fainting, new confusion, vomiting blood, black stools, rapidly worsening weakness or thoughts of self-harm.
Call 999 for a medical emergency. Do not wait for a routine blood-test appointment if you have severe or rapidly worsening symptoms.
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