Which blood tests explain tiredness?
The blood tests that most often explain tiredness are a full blood count, ferritin for iron stores, thyroid function, vitamin B12, folate, vitamin D, HbA1c for blood sugar, kidney and liver function, and inflammation markers. A doctor chooses the right set based on your symptoms. The Online GP by The Wellness offers doctor-led blood panels from £350.
Key points
Tiredness is one of the most common reasons adults see a GP, and women make up around two thirds of patients who present with fatigue.
A study of English primary care records from 2007 to 2017 found men presenting with fatigue had around double the risk of cancer compared with men without fatigue.
Blood tests find a physical cause in a minority of people with tiredness, around 8% in one Dutch trial, so the history and examination matter just as much.
Iron deficiency, an underactive thyroid, low vitamin B12 and raised blood sugar are among the most common treatable causes found on blood tests.
The Online GP by The Wellness offers Core Wellness from £350 and Advanced Health from £650, with every result explained by a doctor.
Which blood tests do doctors check for tiredness?
Doctors usually check a full blood count, ferritin, thyroid stimulating hormone, vitamin B12, folate, HbA1c, kidney and liver function, calcium and an inflammation marker such as CRP. Vitamin D and a coeliac antibody test are added when symptoms point that way. Each test looks for a specific, treatable cause. Ask a doctor on WhatsApp which tests suit you.
Full blood count and ferritin look for anaemia and low iron stores, which are common in women with heavy periods.
Thyroid function looks for an underactive thyroid, which causes tiredness, weight gain and feeling cold.
Vitamin B12 and folate deficiencies cause fatigue and, with B12, tingling or memory problems.
HbA1c picks up diabetes and prediabetes.
Kidney, liver and calcium tests look for less common medical causes.
How often do blood tests find the cause of tiredness?
Blood tests find a physical cause in a minority of people with tiredness. In the VAMPIRE trial of patients with unexplained fatigue, published in 2009, 8% had an illness detectable by blood tests. An earlier BMJ study of 220 patients found laboratory tests contributed to the diagnosis in 19 people.
That does not make testing pointless. For the people with anaemia, an underactive thyroid or diabetes, the test changes everything. For everyone else, a normal panel rules out common medical causes and lets the doctor focus on sleep, stress, mood, alcohol and activity.
"Normal results are not a dead end," says Dr Adel Elalfy, Head of Primary Care at The Online GP by The Wellness. "They tell us where not to look, and that frees the consultation to focus on sleep, workload and mood, which are often the real story."
When is tiredness a sign of something serious?
Tiredness needs prompt assessment if it comes with unexplained weight loss, night sweats, breathlessness, a new lump, bleeding, persistent fever, or if it is severe and getting worse. A study of English primary care from 2007 to 2017 found men presenting with fatigue had around double the cancer risk of men without it.
That study, summarised by NB Medical, included more than 300,000 patients with fatigue. Women made up 67% of the fatigue group, with a peak age of 30 to 49.
Most tiredness has a benign cause. The point of seeing a doctor is to make sure the uncommon serious causes are not missed. Describe your symptoms to a doctor on WhatsApp.
Can low iron cause tiredness even without anaemia?
Yes. Low iron stores, shown by a low ferritin, can cause tiredness, poor concentration, hair shedding and breathlessness on exercise before haemoglobin falls far enough to count as anaemia. A full blood count alone can miss this, which is why ferritin is checked alongside it.
Heavy periods, pregnancy, vegetarian or vegan diets, endurance training and frequent blood donation all raise the risk. Iron deficiency without an obvious cause, particularly in men and in women after the menopause, needs further investigation of the gut.
Our guide to bowel cancer symptoms under 50 explains why iron deficiency anaemia is one of the red-flag signs doctors take seriously.
What happens at a doctor-led tiredness assessment?
A doctor-led tiredness assessment at The Online GP by The Wellness starts with a full history covering sleep, mood, work, periods, diet, alcohol and medicines. The doctor then chooses the blood panel, arranges a draw at TDL, 76 Wimpole Street, and explains every result with a clear plan.
Message the team on WhatsApp to describe your tiredness and how long it has lasted.
A doctor recommends a consultation, a blood panel or both.
You attend 76 Wimpole Street for a morning blood draw.
A GMC-registered doctor reviews and explains your results.
You receive a plan covering treatment, further tests or lifestyle changes.
Measured with precision. Read by expert doctors.
How much do blood tests for tiredness cost?
The Executive Physical at The Online GP by The Wellness starts from £2,995 and is the most comprehensive assessment the clinic offers. Blood panels start at Longevity+ from £1,395, Advanced Health from £650 and Core Wellness from £350. A classic GP appointment starts from £150.
Most people with new tiredness start with Core Wellness, with the doctor confirming the markers it covers. Book a tiredness blood panel on WhatsApp.
Can a doctor tell me if I need blood tests?
Yes. The Online GP by The Wellness offers a free suitability review. Send your main symptoms, how long you have felt tired and any recent results on WhatsApp. A doctor either recommends a blood panel or tells you plainly that a consultation alone is the better first step.
Start your free suitability review on WhatsApp.
Frequently asked questions
Can a vitamin D deficiency cause tiredness?
Yes. Low vitamin D can cause tiredness, muscle aches and low mood, particularly in winter. A blood test shows your level so the doctor can set the right dose.
Should I stop supplements before a blood test?
Biotin, found in many hair and nail supplements, can interfere with thyroid and other results. Tell the doctor about every supplement, as some should be paused for a few days before your test.
Can stress or poor sleep cause tiredness with normal blood tests?
Yes. Stress, poor sleep, low mood and long working hours are common causes of tiredness with normal blood results. The doctor can help address these directly.
How long should I be tired before seeing a doctor?
See a doctor if tiredness lasts more than a few weeks, affects daily life, or comes with weight loss, night sweats, breathlessness or bleeding.
Sources
VAMPIRE trial, Ordering blood tests for patients with unexplained fatigue in general practice, British Journal of General Practice, 2009
Ridsdale L and colleagues, Patients with fatigue in general practice, BMJ, 1993
English primary care fatigue cohort 2007 to 2017, summarised by NB Medical
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