Start with an assessment
Sleep problems, medication effects, stress, low mood and medical conditions can all matter. Investigations should follow the clues.
Beyond 10 minutes · Free guide 03
Tired all the time? Let's ask why.
You do not have to make constant exhaustion your normal.
Updated 12 October 2026 · Adult health education
If fatigue lasts for weeks, affects daily life or comes with other symptoms, book a GP appointment. The right tests depend on your story and examination.
Bring a timeline and explain the impact. Mention sleep, snoring, heavy periods, pregnancy/postpartum changes, diet, medicines, mood and whether activity makes you substantially worse afterwards. Not every cause of fatigue shows up on a blood test.
Blood tests to discuss
Tests are chosen for your symptoms and medical history. This is a discussion guide, not a request for every test.
| Test | Why it may help |
|---|---|
| FBC and ferritin | Check for anaemia or depleted iron stores, especially with heavy periods. |
| Thyroid function | Checks whether a thyroid disorder could be contributing. |
| Glucose or HbA1c | Checks for diabetes when clinically appropriate; mention thirst, frequent urination or weight loss. |
| Kidney and liver function | May help identify other medical contributors to persistent unexplained fatigue. |
| B12 and folate | Consider with compatible symptoms, blood-count changes or deficiency risks, such as restricted diet or absorption problems. |
| Further tests if indicated | Coeliac screening, inflammatory markers, calcium/phosphate or vitamin D may be useful in selected circumstances. |
Your next steps
Do not miss sleep apnoea
Tell your GP about loud snoring, waking unrefreshed, daytime sleepiness or witnessed pauses/gasping during sleep.
Ask what each test is for
A focused set of tests is often more helpful than an expensive panel with no plan for interpreting it.
Make a plan for normal results too
If you still feel unwell, ask what the next step is. Persistent symptoms deserve follow-up even when initial results are reassuring.
Take these questions to your appointment
- Which causes fit my symptoms?
- Which tests are useful for me, and why?
- Could my sleep or medicines be contributing?
- When will we review the results and symptoms?
When to get help
Seek urgent help for chest pain, severe breathlessness or collapse. Contact your GP promptly for unexplained weight loss, bleeding or new neurological symptoms.
Sources and further reading
- NHS: tiredness and fatigue ↗
- NICE NG206: suspected ME/CFS assessment ↗
- NHS: B12 and folate diagnosis ↗
Adapted from Doctor Barbara's educational content, with source-based updates. General information for adults; individual care, pregnancy and children's care need tailored advice. This guide cannot diagnose you or replace your healthcare professional.