Why Am I Tired?
The Advanced Fatigue Blood Test Panel in Central London
Feeling tired all the time is not normal.
Yet many people accept fatigue as part of modern life.
At Marylebone Diagnostic Centre, we see something different.
Persistent tiredness is often a biological signal, not a lifestyle failure.
This guide explains:
- Why you may feel exhausted
- Which blood tests matter
- What fatigue blood tests can (and cannot) diagnose
- When tiredness needs proper medical investigation
Feeling Tired All the Time? You’re Not Alone
Fatigue is one of the most common reasons people book private blood tests in London.
People tell us:
- “I wake up tired”
- “Coffee no longer helps”
- “My brain feels foggy”
- “I sleep, but never feel rested”
Fatigue can affect:
- Concentration
- Mood
- Hormones
- Libido
- Exercise tolerance
- Work performance
Importantly, fatigue has many causes.
Guessing rarely helps. Testing does.
What Does “Fatigue” Actually Mean Medically?
Fatigue is different from simple tiredness. Blood tests can help identify underlying internal drivers, even when symptoms feel vague.
| Term | Meaning |
|---|---|
| Tiredness | Short-term, improves with rest |
| Fatigue | Persistent, disproportionate exhaustion |
| Chronic fatigue | Lasts longer than 6 months |
| Physical fatigue | Body weakness, low stamina |
| Mental fatigue | Brain fog, poor focus |
Understanding the type of fatigue can guide targeted testing and personalised interventions.
Common Medical Causes of Fatigue
Fatigue often comes from multiple overlapping issues, not just one.
The most common causes we detect at MDC:
- Iron deficiency (with or without anaemia)
- Vitamin B12 or folate deficiency
- Vitamin D deficiency
- Thyroid dysfunction
- Hormonal imbalance
- Chronic inflammation
- Liver or kidney stress
- Blood sugar instability
- Early insulin resistance
Many patients have normal GP bloods, yet still feel unwell.
That is usually because the right markers were not checked.
The “Why Am I Tired?” Advanced Fatigue Panel – What We Test
Core Fatigue Blood Markers
This panel is designed to look beyond basic screening, identifying nutritional, hormonal, metabolic, and inflammatory drivers of persistent fatigue.
| Test | Why It Matters |
|---|---|
| Full Blood Count (FBC) | Detects anaemia, infection patterns |
| Ferritin | Iron stores (often missed) |
| Vitamin B12 | Energy production, nerve function, cognition |
| Folate | Red blood cell formation |
| Vitamin D | Immune and muscle function |
| Thyroid Panel (TSH, FT4 ± FT3) | Metabolic and energy regulation |
| Liver Function Tests | Detoxification and metabolic load |
| Kidney Function (Urea, Creatinine, eGFR) | Fluid balance and toxin clearance |
| CRP | Systemic inflammation |
| HbA1c | Long-term blood sugar control |
This combination provides a systems-level view of fatigue, helping clinicians identify correctable contributors rather than treating symptoms in isolation.
Why GP Blood Tests Often Miss the Cause of Fatigue
GP testing is designed for disease detection, not optimisation.
Common limitations:
- Ferritin not tested unless anaemia is severe
- “Normal” ranges are wide
- Early deficiencies are dismissed
- Symptoms are assessed separately from bloods
At MDC, we look at:
- Functional ranges
- Patterns, not isolated numbers
- Symptoms alongside results
Fatigue often sits between normal and abnormal.
Iron Deficiency Without Anaemia – A Major Hidden Cause
You can have:
- Normal haemoglobin
- Low ferritin
- Severe fatigue
Low iron stores affect:
- Oxygen delivery
- Brain function
- Exercise tolerance
- Mood stability
This is especially common in:
- Women
- Vegetarians
- Endurance athletes
- People with gut absorption issues
Ferritin testing is essential.
Vitamin B12 & Folate – Energy at a Cellular Level
Vitamin B12 deficiency may cause:
- Fatigue
- Brain fog
- Pins and needles
- Memory problems
Importantly:
- Levels can be “low-normal” and still symptomatic
- Absorption issues are common
- Long-term deficiency affects nerves
Folate works alongside B12.
Testing one without the other gives an incomplete picture.
Thyroid Problems and Fatigue
Your thyroid controls:
- Energy production
- Body temperature
- Weight regulation
- Heart rate
Even mild thyroid dysfunction can cause:
- Exhaustion
- Cold intolerance
- Brain fog
- Low mood
Many patients have:
- “Normal” TSH
- Sub-optimal FT4 or FT3
- Ongoing symptoms
That is why complete thyroid panels matter.
Hormones and Fatigue (Men & Women)
Hormonal imbalance is a major fatigue driver.
In men:
- Low testosterone
- High SHBG
- Cortisol dysregulation
In women:
- Oestrogen imbalance
- Progesterone deficiency
- Perimenopausal hormone shifts
Fatigue is often the first symptom, long before cycles change or libido drops.
Hormone testing can be added to your fatigue panel when appropriate.
Inflammation, Liver & Metabolic Stress
Low-grade inflammation drains energy.
CRP helps identify:
- Chronic inflammatory load
- Overtraining
- Metabolic stress
Liver and kidney markers matter because:
- Detoxification uses energy
- Hormones are metabolised in the liver
- Metabolic overload causes fatigue
This is especially relevant for:
- High-stress professionals
- GLP-1 users
- People on long-term medication
What This Panel Can and Cannot Tell You
This panel CAN:
- Identify biological causes of fatigue
- Detect deficiencies early
- Guide targeted treatment
- Reduce trial-and-error supplements
This panel CANNOT:
- Diagnose chronic fatigue syndrome alone
- Replace full clinical assessment
- Identify sleep disorders directly
- Diagnose mental health conditions
Blood tests are a starting point, not the whole story.
When Should You Book a Fatigue Blood Test?
You should consider testing if fatigue lasts:
- Longer than 4–6 weeks
- Despite rest
- Despite good sleep
- Despite “normal” GP tests
Especially if you have:
- Brain fog
- Low motivation
- Poor exercise recovery
- Mood changes
- Weight changes
Why Choose Marylebone Diagnostic Centre?
- Results within 24–42 hours
- On-site consultant review
- Private suites
- Discreet and confidential care
- CQC-accredited and aligned with Marylebone High Standard
- Optional teleconsultations for results
📍 73 Baker Street, London W1U 6RD
🚇 5-minute walk from Baker Street tube
🕗 Monday–Saturday, 8:00–16:00
📞 +44 7495 970109
Frequently Asked Questions
Stress can worsen fatigue, but blood tests often reveal underlying contributors such as nutrient deficiencies, inflammation, or hormonal imbalance.
Not always. Many fatigue drivers sit within reference ranges and require clinical interpretation.
Most fatigue panels return results within 24–42 hours, depending on the test profile.
Yes. Hormone testing is commonly added based on symptoms and clinical context.
Book Your “Why Am I Tired?” Panel Today
Fatigue is not something you should ignore.
It is information.
Understanding the cause allows:
- Targeted treatment
- Faster recovery
- Better long-term health
