When Fatigue Needs Medical Assessment
- Persisting for more than 4 weeks without an obvious cause (recent illness, poor sleep, major stress)
- Accompanied by unexplained weight loss
- With unusual bruising or bleeding
- With fevers or night sweats
- Significantly affecting daily function and quality of life
- New shortness of breath or palpitations alongside fatigue
The Standard Fatigue Blood Test Panel
| Test | What It Checks |
|---|---|
| FBC (full blood count) | Anaemia, infection, blood disorders |
| TSH (thyroid) | Underactive or overactive thyroid |
| Fasting glucose / HbA1c | Diabetes |
| Ferritin (iron stores) | Iron deficiency, even without anaemia |
| Vitamin B12 and folate | Deficiency causing fatigue and neurological symptoms |
| Vitamin D | Very common deficiency linked to fatigue |
| U&Es (kidney function) | Kidney disease |
| Liver function tests | Liver disease |
| CRP/ESR | Inflammatory or infectious causes |
| Coeliac screen (tTG-IgA) | Coeliac disease — often presents as fatigue alone |
If All Tests Are Normal
Persistent unexplained fatigue with normal tests may still be a real, significant condition — such as ME/CFS, depression, sleep disorders, or a stress-related condition. Normal blood tests don't mean nothing is wrong; further specific assessment may be needed.Push for a Full PanelIf you present with fatigue and only get a single test (e.g. just a full blood count), it's reasonable to ask your doctor whether the full standard fatigue panel (above) has been considered, as many treatable causes are easily missed with partial testing.
What is the most common cause of fatigue found on testing?
Iron deficiency (with or without anaemia) and vitamin D deficiency are among the most commonly identified treatable causes, followed by thyroid dysfunction, especially in women.
Can depression cause physical fatigue?
Yes, absolutely — depression very commonly presents with profound physical fatigue, sometimes without significant low mood being the presenting complaint. It's always worth considering alongside physical causes.
Should I get a full body MRI if I'm just tired?
No — this is rarely indicated or useful for isolated fatigue without other specific symptoms or red flags. The standard blood panel above identifies the overwhelming majority of treatable causes.
Medical Disclaimer: This page is for general education only and does not replace professional medical advice. Always consult a qualified healthcare provider.