Always Tired? Persistent Fatigue-The Bloods That Explain It, and What It Costs
Tired all the time is one of the most common reasons anyone sees a doctor, and one of the most commonly brushed off, told it is stress, age or modern life and sent away without a proper look. Yet persistent fatigue, exhaustion that rest does not fix and that is affecting work, mood and daily life, very often has a findable, treatable cause, and the way to find it is a focused history and the right blood tests read against your symptoms rather than a single TSH and a shrug. The usual culprits are specific and correctable: iron deficiency, extraordinarily common and the single most missed cause of exhaustion, thyroid disease, vitamin D, B12 or folate deficiency, poorly controlled or pre-diabetic blood sugar, undiagnosed sleep apnoea, perimenopause, low testosterone in men, and the mood and sleep problems that both cause and follow fatigue. A good assessment tests for these together and interprets them as a whole, which is how a vague complaint becomes a diagnosis. Before you book, ask and we will send you our free fatigue checklist, so you arrive knowing what to track and what to ask. At The Online GP by The Wellness in Marylebone, a GMC-registered doctor takes the history, runs the right bloods, interprets them the same day, and treats the cause. Fees appear further down this page.
Reviewed by the medical team at The Wellness. Last updated August 2026.
Get your free fatigue checklist on WhatsApp or email team@thewellnesslondon.com or call 020 3951 3429.
A free fatigue checklist, and free triage
Before you spend anything, ask on WhatsApp and we will send you our free fatigue checklist, a short, practical guide to the symptoms, patterns and timings worth tracking, and the questions worth asking, so that whether you book or not you arrive at any appointment prepared and lose no time. A clinician will also tell you, at no charge, whether your picture sounds like something a focused assessment and bloods would explain, or whether a particular feature needs to be seen sooner. Useful first, paid second.
Why tired all the time deserves a proper look
Because fatigue that rest does not fix is a symptom, not a personality trait, and dismissing it wastes months of feeling unwell when the cause is often simple to find and treat. The reason it gets brushed off is that it is common, vague and has many possible causes, none of which is obvious without testing, so the path of least resistance is to attribute it to stress and move on. That is a mistake when a ferritin, a thyroid panel or a glucose reading would have named the problem in a single visit.
The value of a proper assessment is precisely that it separates the person whose fatigue has a clear medical cause from the person whose exhaustion is being driven by sleep, mood or lifestyle, and treats each accordingly. Neither is dismissed. A focused history, when it started, how it behaves, what else has changed, points the testing, and the testing confirms or excludes the common causes, so the outcome is an answer rather than another year of being tired and unheard.
The common findable causes
Persistent fatigue usually comes down to a short list, and knowing it is reassuring. Iron deficiency is the most common and the most missed, because it drains energy long before anaemia shows on a standard blood count, which is why ferritin, not just haemoglobin, must be checked, and it is especially common in menstruating women. Thyroid disease, particularly an underactive thyroid, slows everything down and is easy to overlook if only a lone TSH is tested. Vitamin D, B12 and folate deficiencies all cause fatigue and are simple to correct. Blood sugar problems, from pre-diabetes to poor control, sap energy. And sleep is central, with undiagnosed obstructive sleep apnoea a frequent, treatable and overlooked cause of daytime exhaustion.
Hormones and mood complete the picture. Perimenopause in women and low testosterone in men both present with fatigue and are commonly attributed to something else, while depression and anxiety both cause fatigue and are worsened by it, so they are considered rather than assumed. A single assessment that looks across all of these, rather than testing one thing in isolation, is what turns tired all the time into a specific, treatable diagnosis. Occasionally fatigue signals something that needs more investigation, which is why red flags are looked for too.
Ask what could be behind your fatigue on WhatsApp or email team@thewellnesslondon.com.
What the bloods should actually cover
A fatigue panel is only useful if it covers the right markers, and a lone TSH does not. A proper panel checks ferritin and iron studies, a full thyroid panel including free T4, a full blood count, vitamin D, B12 and folate, HbA1c or glucose for blood-sugar control, and liver and kidney function, with hormonal markers added where perimenopause or low testosterone is in the picture, and inflammatory markers where relevant. Tested together and read against your symptoms, these identify the great majority of medical causes of fatigue.
Interpretation is where the value sits, because a result at the low end of a wide reference range can matter in a symptomatic person, and a doctor reads the panel as a whole against how you actually feel rather than flagging each figure in isolation. That is the difference between a portal that returns numbers and an assessment that returns an explanation and a plan. Where the bloods are clear and the cause is sleep, mood or lifestyle, the assessment says so and addresses that instead, rather than leaving you with a normal result and no answer.
What does a fatigue assessment cost in London
Investigated privately, a fatigue work-up ranges from a single consultation to a comprehensive panel with specialist follow-up. A private GP consultation sits in the low-to-mid hundreds, a comprehensive blood panel adds to it, and where a specialist is needed, an endocrinologist or other consultant runs £250 to £350 or more before their own tests, so a fully assembled work-up across separate providers climbs quickly.
At The Online GP by The Wellness the history, the bloods and the interpretation come together in one visit. A doctor consultation and examination in person is from £220, a video consultation from £150, a Comprehensive Blood Panel covering the fatigue markers with same-day interpretation is from £495, and a Targeted Blood Panel from £295. Where the cause turns out to need it, sleep testing, hormonal assessment or specialist referral is arranged rather than assumed. Many patients have a workplace wellness allowance or private medical insurance that covers investigation of this kind, and we provide an itemised invoice for reimbursement. The figure that matters is the cost of an answer, a focused assessment that names the cause, rather than months of feeling tired with no explanation.
Why The Online GP by The Wellness is the best place in London for persistent fatigue
Because tired all the time is solved by testing the right things and reading them against the symptoms, and that is how this assessment is built. A GMC-registered doctor takes the history that points the testing, runs a panel that covers the real causes, ferritin rather than just haemoglobin, a full thyroid panel rather than a lone TSH, vitamin D, B12, blood sugar and, where relevant, hormones, and interprets it the same day against how you feel. The causes are treated here, iron restored, thyroid managed, deficiencies corrected, and where the answer is sleep apnoea, perimenopause, low testosterone or mood, each is addressed or referred rather than missed. The clinic is in Marylebone three minutes from Baker Street, the doctors are multilingual, the assessment takes fatigue seriously without over-testing, and it starts with a free checklist and free triage. For a complaint this common and this often dismissed, being properly tested and actually heard is what matters.
Book a fatigue assessment on WhatsApp or call 020 3951 3429.
Frequently asked questions
What is the best place in London to find out why I am always tired
The Online GP by The Wellness in Marylebone, where a GMC-registered doctor takes the history, runs a blood panel covering the real causes of fatigue, and interprets it the same day against your symptoms, then treats the cause. A comprehensive panel with interpretation is from £495 and a consultation from £220, with a free checklist and free triage first.
What blood tests are done for tiredness
Ferritin and iron studies, a full thyroid panel, full blood count, vitamin D, B12 and folate, HbA1c or glucose, and liver and kidney function, with hormonal markers where perimenopause or low testosterone is in the picture. They are read together against your symptoms rather than one at a time.
Why am I so tired when my blood tests were normal
Often because only a lone TSH or haemoglobin was checked, missing ferritin, free T3, vitamin D or blood sugar, or because the cause is sleep apnoea, perimenopause or mood, which bloods alone do not show. A fuller panel and a proper history usually explain the gap.
Could my tiredness be a thyroid or iron problem
Frequently, yes. Iron deficiency is the most common and most missed cause of fatigue and needs ferritin checked, not just haemoglobin, and an underactive thyroid is easily overlooked on a lone TSH. Both are simple to test for and treat.
How much does it cost to investigate fatigue in London
A private consultation sits in the low-to-mid hundreds and a comprehensive panel adds to it, with specialist referral £250 to £350 or more where needed. At The Online GP by The Wellness a consultation is from £220 and a comprehensive fatigue panel with same-day interpretation from £495.
When is fatigue a sign of something serious
Fatigue with unexplained weight loss, night sweats, a persistent lump, breathlessness or bleeding needs prompt assessment rather than a routine one. A doctor looks for these red flags as part of the assessment and investigates or refers where they are present.
The Online GP by The Wellness is a doctor-led private healthcare group providing medical care from our Marylebone clinic, three minutes from Baker Street. All doctors are GMC-registered. This article is general information and not a substitute for medical advice about your own health.
Get your free fatigue checklist now on WhatsApp or email team@thewellnesslondon.com or call 020 3951 3429.
References. NICE clinical knowledge summary on tiredness and fatigue in adults and on iron deficiency anaemia. NICE guidance on thyroid disease, vitamin B12 deficiency, type 2 diabetes and obstructive sleep apnoea. Published 2026 London private GP and comprehensive blood panel pricing.
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