Blood Tests for Fatigue: Finding the Cause of Your Tiredness
Fatigue is one of the most common health complaints, yet it is also one of the most difficult to resolve without proper investigation. It is also the most common reason people get in touch with us, and they have often lived with it for so long that it feels normal. Feeling persistently tired is not normal — it is your body signalling that something needs attention.
The causes of chronic fatigue are wide-ranging: nutritional deficiencies, hormonal imbalances, thyroid dysfunction, poor sleep quality, chronic inflammation, blood sugar dysregulation, and underlying medical conditions can all contribute. What makes fatigue particularly frustrating is that these causes often overlap, and multiple factors may be at play simultaneously. A comprehensive blood test is one of the most effective first steps you can take when dealing with persistent tiredness.
Rather than guessing or trying one supplement after another, blood testing gives you objective data about your body's internal state. At Wellth, our fatigue-focused panels are designed to test the most common biological causes of tiredness in a single blood draw.
Key Biomarkers to Investigate Fatigue
Iron
Iron studies (ferritin, serum iron, transferrin, transferrin saturation) are among the first markers to check. Ferritin is your body's iron storage protein — levels can be low enough to cause fatigue long before you develop full anaemia.
Full blood count
A complete blood count (CBC) reveals whether you have anaemia (low haemoglobin or red blood cell count) and what type it might be.
The thyroid
Thyroid function tests (TSH, Free T4, Free T3) are essential, as hypothyroidism is one of the most common and treatable causes of fatigue.
Vitamin D, B12 and folate
Vitamin D levels should always be checked, particularly in Sweden where deficiency is widespread and strongly associated with tiredness and low mood. Vitamin B12 and folate are critical for energy production and red blood cell formation — deficiency in either can cause fatigue and cognitive difficulties.
Blood sugar
Blood glucose (fasting glucose and HbA1c) identifies blood sugar dysregulation that can cause energy crashes.
Inflammation and cortisol
Inflammatory markers (CRP, ESR) may reveal chronic low-grade inflammation contributing to fatigue. Cortisol helps assess whether adrenal stress response is a factor.
Signs You Should Get Blood Tests for Fatigue
- Feeling tired most days despite sleeping 7 to 9 hours
- Needing caffeine to function through the day
- Waking up feeling unrefreshed or exhausted
- Afternoon energy crashes or needing to nap
- Fatigue that has persisted for more than 4 weeks
- Tiredness accompanied by brain fog or poor concentration
- Reduced exercise tolerance or feeling breathless with light activity
- Dizziness or lightheadedness when standing up
- Feeling tired alongside other symptoms like hair loss, weight gain, or mood changes
- Previous blood tests were normal but you still feel exhausted
What Your Results Might Show
Low ferritin
Low ferritin (even with a normal haemoglobin) is one of the most common findings in fatigued patients, particularly women with menstrual periods. Ferritin below 30 micrograms per litre is associated with fatigue symptoms, even though many lab reference ranges classify this as normal. Your Wellth report uses optimal ranges, not just standard ones.
The thyroid
An underactive thyroid (elevated TSH with low Free T4) can cause profound fatigue, and even subclinical hypothyroidism (mildly elevated TSH with normal Free T4) is associated with tiredness in some people.
Vitamin D and B12
Low vitamin D is extremely common in Sweden and contributes to fatigue, muscle weakness, and low mood — particularly during the darker months. Low vitamin B12, especially in those following plant-based diets, can cause fatigue alongside neurological symptoms.
Blood sugar
Elevated fasting glucose or HbA1c may indicate prediabetes or insulin resistance, which commonly causes energy fluctuations throughout the day.
More than blood tests
Blood tests are only part of the picture. Late nights, long gaps between meals and a lot of coffee can all leave you tired, even when every result is normal. We start with sleep, food and daily life, and the blood tests then show what lies underneath.
Your report
Your report will identify which findings are most likely contributing to your fatigue and prioritise recommendations accordingly.
Frequently Asked Questions
What blood tests should I ask for if I am always tired?
My previous blood tests were normal but I am still tired. What should I do?
How quickly can blood test results explain my fatigue?
Can fatigue be caused by more than one thing at the same time?
When should I see a doctor about tiredness?
Reviewed by
Wellth Team
Wellth
Our content is written and reviewed by Wellth, and fact-checked against peer-reviewed research and current Swedish clinical guidelines.
Learn more about our team →Important to know
Wellth does not diagnose or treat disease. We work with diet, lifestyle and preventive health, alongside the care you already have.
Our reports and sessions do not replace medical advice, and a test result should not be read as a diagnosis. We use both standard healthcare reference ranges and optimal ranges. A value can therefore be normal by healthcare standards and still fall outside the range associated with good health. That does not mean disease, but it can be a chance to act early.
Supplements are only recommended by a nutritional therapist as part of a consultation, never automatically from a test result.
If anything in your results needs to be looked at by a doctor, we will tell you clearly. Contact your healthcare provider if you are worried about your health. Call 1177 for advice, or 112 in an emergency.