Why Am I So Tired? The Blood Tests You Actually Need
Reviewed by Dr Lauren Holland • Marylebone Diagnostic Centre, London
Fast results within 24 – 42 hours. Westminster residents receive 20% off.
Feeling constantly tired is one of the most common health issues among adults in London. Long working hours, stress, poor sleep, diet and underlying medical conditions can all contribute. However, many people struggle to understand why their energy levels are low even when their routine blood tests appear “normal”.
At Marylebone Diagnostic Centre (MDC), we often see patients who feel exhausted but have never had a comprehensive fatigue work-up. Fatigue can come from many medical causes that require targeted testing. Below is a clear clinical guide to the blood tests that help identify the root cause.
Iron, B12 and Folate Deficiency
Low iron, vitamin B12 or folate can cause tiredness, dizziness, pale skin, headaches and shortness of breath. These nutrients help transport oxygen around the body. Even slight deficiencies can lead to fatigue.
Recommended tests: Full Blood Count, Ferritin, Iron Studies, Vitamin B12 and Folate.
MDC offers these as part of the Fatigue and Anaemia Profile.
Thyroid Function
The thyroid gland controls metabolism. If it is underactive, you may feel tired, cold, depressed, or notice weight gain. If it is overactive, you may feel anxious, sweaty or have a fast heartbeat, but still be tired.
Recommended tests: TSH, Free T4, and Thyroid Antibodies when indicated.
Inflammation and Hidden Infection
Low-grade inflammation or lingering infections can cause persistent tiredness.
Recommended tests: CRP, ESR, White Cell Count and differential.
These tests can indicate whether your immune system is reacting to infection or inflammation.
Blood Sugar and Metabolic Health
Fluctuating blood sugar levels can make you feel weak, shaky or tired after meals. Insulin resistance may also contribute to ongoing fatigue.
Recommended tests: HbA1c, Fasting Glucose, and a Lipid Profile.
MDC’s Cardiac Profile (MLCP2) includes these markers along with other cardiovascular tests.
Hormonal Causes of Fatigue
Hormone changes can affect sleep, motivation and mental clarity.
In women, fluctuations in oestrogen, progesterone, FSH and LH can cause tiredness, especially around perimenopause and menopause.
In men, low testosterone may cause low energy, low mood and reduced muscle strength.
MDC provides both Male Hormone Panels and Female Hormone Panels.
Vitamin and Mineral Deficiencies
Vitamin D, Magnesium and Zinc are among the most common deficiencies in London. Low levels can cause muscle aches, poor recovery, anxiety, low mood and low energy.
MDC provides blood tests for vitamins and minerals, as well as the Hair Mineral Analysis to assess long-term mineral balance.
Stress, Cortisol and Sleep Quality
Chronic stress can keep cortisol elevated, disrupting sleep and creating ongoing tiredness.
Cortisol testing is available at MDC and can help identify whether stress is affecting energy levels.
When You Should Consider Testing
- You should arrange blood tests if you experience any of the following:
- Persistent tiredness for more than two weeks
- Morning fatigue despite adequate sleep
- Hair loss or pale skin
- Brain fog, low concentration or irritability
- Unexplained weight changes
- Cold hands or feet
- Fast heart rate or shortness of breath
- Recurrent infections
The Marylebone Diagnostic Centre Approach
All tests at MDC are processed under QC-validated laboratory standards. Results are delivered within 24 – 42 hours and can be reviewed with a clinician who will explain the findings and advise on the next steps. You will receive a clear, actionable plan based on your results.
Book Your Fatigue and Wellness Blood Test in London
Marylebone Diagnostic Centre
73 Baker Street, London W1U 6RD
Tel: +44 7495 970109
Monday to Saturday, 08:00–16:00
5-minute walk from Baker Street Station
Westminster residents receive 20% off all profiles.
