Wellness . Symptoms guide
Persistent Fatigue: A Blood Test Roadmap
Persistent fatigue (more than 4 to 6 weeks) deserves a structured work-up. The most common reversible drivers are iron deficiency (often before frank anaemia), vitamin D deficiency, B12 deficiency, thyroid dysfunction and low testosterone in men. A single panel covers all of these and removes the need for repeated GP visits to add markers one at a time.
This patient information is being clinically reviewed by our team. The factual content draws on UK guidance (NHS, NICE, British Association of Dermatologists, British Society for Sexual Medicine where cited).
What this might be
- Iron deficiency. Most commonly missed reversible cause; ferritin reveals it before anaemia appears.
- Thyroid dysfunction. Both directions cause fatigue.
- Vitamin D deficiency. Very common in the UK, especially winter to spring.
- B12 deficiency. Especially in vegan, vegetarian, or older patients.
- Low testosterone (in men). Both fatigue and low mood are common signs.
- Post-viral fatigue. CRP and ESR help context.
When to seek urgent advice
If any of the following apply, please contact your GP, NHS 111, or A&E in the first instance rather than waiting for private bloodwork.
- Unexplained weight loss
- Night sweats
- New persistent lumps
- New severe headache
- Blood in stool or urine
Common features that suggest this
- Tiredness lasting 4 or more weeks
- Not refreshed by sleep
- Reduced exercise tolerance
- Concurrent low mood, brain fog or hair changes
Recommended tests
Same-day appointments at our Harley Street clinic, results clinician-reviewed.
Need a marker not in these panels? Build a custom panel and a GMC-registered clinician will design one for you.
Testing advice
Morning slot helps if hormones are included. Fasting recommended for the General Wellness panel (cholesterol, HbA1c). No fasting for hair or hormone panels.
Common questions
Which panel covers most causes?
General Wellness is the best single starting panel for unexplained fatigue. If you have hair-specific symptoms too, Hair Loss Essentials adds the relevant markers without duplicating cost.
What if all my results come back normal?
That itself is useful. It rules out the common medical causes, focusing attention on sleep, lifestyle, mental health, or rarer conditions that require specialist referral.
Related symptoms
Sources and further reading
This page provides general information only and is not a substitute for medical advice. A GMC-registered clinician will review your results and tailor any recommendations to you personally.