Test it in Chiswick: our Tired All The Time blood test costs £159, with your result explained in person by a practitioner. No GP referral needed. Book this test or call 020 4515 0000. Read blood tests for brain fog.
Why tiredness is worth testing
Fatigue is one of the most common reasons people see a GP and one of the hardest symptoms to pin down, because almost everything causes it. A focused set of blood tests does not explain every case, but it finds the causes that are both common and straightforward to treat, and it rules them out quickly when they are not the answer.
The tests that matter most
Full blood count. Anaemia, a shortage of red cells or haemoglobin, is the classic cause of tiredness and breathlessness on exertion. It is especially common in women with heavy periods, in vegetarians and vegans, and in older adults.
Ferritin. Iron stores can be low, causing fatigue and poor concentration, well before the full blood count shows anaemia. Ferritin is the marker that catches this early.
Vitamin D. Widespread in the UK, particularly from October to March, and associated with tiredness, low mood and muscle aches. Easily corrected.
B12 and folate. Deficiency causes fatigue, pins and needles, memory problems and low mood. More common in people on a plant-based diet, on long-term acid-reducing medication or metformin, and in older adults.
Thyroid function. An underactive thyroid slows everything down: tiredness, weight gain, feeling cold, dry skin, low mood. It is common, often missed, and treatable.
HbA1c. Undiagnosed diabetes or pre-diabetes causes tiredness, thirst and needing to pass urine more often.
Kidney and liver function. Less often the cause, but chronic kidney disease and liver problems both cause fatigue and are silent otherwise.
Blood tests for tiredness and weight gain
When tiredness comes with weight gain, the most useful starting points are a thyroid blood test (TSH and free T4), because an underactive thyroid causes both, and an HbA1c test for blood sugar and insulin resistance. Ferritin and a full blood count matter too, because low iron saps energy and makes activity harder. In women, a female hormone panel can help when symptoms suggest polycystic ovary syndrome or the perimenopause. In men, testosterone is worth checking. A cortisol test is only useful alongside other signs of a cortisol problem, such as easy bruising, thin skin or a rounder face, and needs a doctor to interpret. Most weight gain with tiredness is not caused by a blood abnormality, so normal results point back to sleep, diet, activity, stress and medication.
Sometimes useful
CRP for inflammation or a lingering infection. Coeliac antibodies if there are digestive symptoms or unexplained iron deficiency. Testosterone in men with fatigue, low mood and reduced drive. A female hormone panel if symptoms cluster around perimenopause. Magnesium and calcium are occasionally relevant but rarely the explanation on their own.
If everything is normal
That is useful information. It moves the search towards sleep quality, sleep apnoea if you snore or wake unrefreshed, stress and workload, mood, alcohol, medication side effects and post-viral fatigue. A normal panel should not be repeated in the hope of a different answer; it should redirect the conversation.
At Omnia
Our Tired All The Time blood test (43 biomarkers, £159) covers every core marker above except a full liver profile, in one draw at our Chiswick clinic. For a smaller starting point, see every blood test and price, including single tests for vitamin D (£59), vitamin B12 (£49) and a full blood count (£59). We review the results with you, and where the tests are normal we help you think through the non-blood causes rather than leaving you with a clean report and no plan.