Raised or abnormal blood count investigation (Investigation of an abnormal full blood count)
The set of tests used to find out why a blood count is abnormal, ranging from repeat blood tests to, sometimes, a bone marrow test.
✓ Medically reviewed by a GMC-registered consultant · last reviewed September 2026 · next review September 2027 · how we review
In short
- This is an investigation to explain why a blood count is abnormal, not a diagnosis in itself.
- An abnormal count is common and often has a harmless or temporary cause, though sometimes it needs treatment.
- The work-up is step by step — often repeat blood tests first, then further tests, and sometimes a bone marrow test, depending on findings.
- Some results take time, especially genetic or marrow tests; ask what each result would change and what happens if it is normal, abnormal or unclear.
A plain-English summary. The detail — including risks and recovery — is below.
At a glance
A general guide. Your specialist will give you advice for your situation.
Can explain why a blood count is abnormal and provide reassurance when the cause is harmless
Doing extensive private testing before simple, cheaper steps (such as repeating the blood test) have been tried.
You can carry on as normal. There may be minor bruising where the needle went in.
A clear explanation of each result and the specific next step.
You can carry on as normal. There may be minor bruising where the needle went in.
Some results come back within days; others, such as genetic or marrow tests, take longer. Ask how and when you...
You may have soreness and bruising at the site for a few days. Most people go home the same day and return to...
Your doctor explains what the results mean and the next step, which may be reassurance, treating a cause...
What it is
A full blood count is a common blood test that measures your red cells, white cells and platelets. When one or more of these is too high, too low or abnormal, your doctor may arrange more tests to find out why. This guide is about that investigation, not about any single diagnosis.
An abnormal blood count is common and often has a harmless or temporary explanation — for example a recent infection, inflammation, pregnancy, smoking, dehydration, or a reaction to medicine. Sometimes it points to a condition that needs treatment, including, in a minority of cases, a blood disorder or blood cancer.
The investigation is a step-by-step process. It often starts with repeating the blood test and reviewing your symptoms, medicines and history, then adds further blood tests, and sometimes a scan or a bone marrow test, depending on what is found. A blood film (looking at the cells under a microscope) and genetic tests can give extra information.
The aim is to explain the abnormal result safely, neither missing something important nor causing alarm or unnecessary tests. Many people are reassured after a few tests; others need closer follow-up or treatment. A normal or improving result is itself useful information.
Types, options & approaches
There may be different ways to do this. The right approach depends on the clinical question and your circumstances.
Some tests used in the work-up
| Test | What it shows | When it is used |
|---|---|---|
| Repeat blood count | Whether the change is persistent | Almost always, as a first step |
| Blood film | The appearance of the cells | To look for clues about the cause |
| Genetic blood tests | Specific changes (such as JAK2) | When certain conditions are suspected |
| Bone marrow test | What the marrow is producing | When needed to confirm a diagnosis |
Not everyone needs all of these. The pathway is guided by your results, symptoms and history, and your team will explain why each test is suggested.
Preparing for your test
- Ask which part of your blood count is abnormal and what the likely explanations are, so you know what is being looked for.
- Bring a list of your medicines and supplements, as some affect blood counts.
- Mention recent infections, inflammation, pregnancy, smoking, alcohol, and any family history of blood conditions.
- Bring any previous blood results you have, as trends over time are very useful.
- Ask whether you need to do anything before a test, such as timing, though most blood tests need no special preparation.
- For a possible bone marrow test, ask about what it involves, arranging someone to be with you, and pain relief.
- Ask how and when you will get each result, and who to contact with questions.
What happens
Most of the investigation involves straightforward blood tests, taken from a vein in your arm, sometimes more than once over a period of time. A laboratory may also examine a blood film under the microscope, and run further tests on the same or a new sample.
Your doctor reviews the results alongside your symptoms, examination, medicines and history. Many abnormal counts are explained at this stage — for example by infection, inflammation, iron or vitamin levels, smoking or medicines — and may simply need rechecking or treating the cause.
If the picture is unclear or suggests a blood disorder, you may be referred to a haematologist and may have further tests, such as genetic blood tests or a scan. A small number of people need a bone marrow test, where a sample is taken from the back of the pelvis using a needle under local anaesthetic; you can usually go home the same day.
Throughout, the aim is to work things out safely and proportionately, doing enough tests to explain the result without over-investigating. You should be told what each result means and what the next step is.
Is this test right for me?
A good consultation should explore whether it's the right choice for you now — including reasons to wait or consider something else.
May not be suitable if…
- Doing extensive private testing before simple, cheaper steps (such as repeating the blood test) have been tried.
- Relying on a single abnormal result as a diagnosis without considering the trend and the whole picture.
- A bone marrow test when simpler tests have not yet been done or would answer the question.
- Investigating in isolation when urgent symptoms (such as signs of serious infection or bleeding) need same-day care instead.
- Wide 'screening' panels marketed to healthy people, which often raise more questions than they answer.
Delay or rearrange if…
- A recent infection, inflammation or pregnancy could explain the result and a repeat test would clarify it.
- A medicine or supplement that affects blood counts has not yet been reviewed.
- Previous results that would show a trend are not yet available.
- You are acutely unwell and need urgent assessment rather than a routine work-up.
- Key earlier results are still awaited before deciding on further tests.
Alternatives to discuss
- Simply repeating the blood count after an interval, rather than immediate extensive testing.
- Treating an obvious cause, such as iron or vitamin deficiency or infection, and rechecking.
- Watchful monitoring with periodic blood tests for a borderline, stable result.
- Referral to an NHS haematology service rather than private testing.
- No further testing if the cause is clear and harmless.
Before you decide
Use this as a shared-decision checklist. The aim is not just “can this be done?”, but whether it is right for you, now, with the risks and alternatives clearly understood.
What matters most to me?
Think about symptoms, daily life, work, caring responsibilities, sport, fertility, travel, appearance and anxiety — the right choice depends on your priorities, not just the medical facts.
What are all my options?
Ask about waiting, monitoring, medicines, rehabilitation, a smaller or larger procedure, a different test, NHS referral, or a second opinion where that would help.
What would make me pause?
Active infection, pregnancy, unstable medical problems, smoking, medicines that increase bleeding, poor support at home, or feeling pressured are all reasons to slow down and get tailored advice.
What happens if I do nothing today?
For some problems, waiting is safe; for others, delay can make treatment harder. A good consultation should explain the trade-off in plain English.
Comfort, sedation or contrast choices
If local anaesthetic, sedation, contrast or pain relief is used, ask what is planned, why, and what it means afterwards.
Benefits
- Can explain why a blood count is abnormal and provide reassurance when the cause is harmless
- Can find treatable causes, such as iron or vitamin deficiency, infection or inflammation
- Can detect a blood disorder or blood cancer earlier, when that is the cause
- Helps avoid both missing something important and doing unnecessary treatment
- Trends over repeated tests give more information than a single result
- Guides whether monitoring, treatment or simply reassurance is needed
Risks & complications
- Discomfort or bruising from blood tests
- Worry while waiting for results
- Needing repeat tests, which can feel inconvenient or unsettling
- Sometimes finding an unrelated, incidental abnormality that needs further thought
- An inconclusive result that needs more tests or a period of monitoring
- A borderline result that is hard to interpret and may cause uncertainty
- Being referred on when the cause turns out to be harmless (a 'false alarm')
- Discomfort, bruising or, rarely, bleeding or infection from a bone marrow test if one is needed
- A delay or repeat if a sample is inadequate
- Very rarely, a serious complication from a bone marrow test, which is performed by trained staff to minimise this
The investigation itself is low risk — mostly blood tests. The main downsides are anxiety while waiting, the chance of an inconclusive or borderline result, and occasionally finding something unrelated. A bone marrow test, needed only by some, is generally safe but can cause discomfort, bruising and, rarely, bleeding or infection. The most useful questions are what each result would change, and what happens if it comes back normal, abnormal or unclear.
Published figures to discuss
How often an abnormal blood count turns out to be serious depends heavily on which cells are affected, how abnormal the result is, your age, your symptoms and your history, so a single figure is not meaningful. Many abnormal counts have benign or temporary causes. Complication rates from a bone marrow test are low but vary, and inadequate samples occasionally mean a repeat. Because robust, generalisable percentages are limited and so situation-dependent, this guide avoids quoting exact rates; ask your clinician what your specific result is likely to mean.
| Figure | Reported range | How to interpret it | Source / confidence |
|---|---|---|---|
| Transient abnormality over-investigated | Common | Infection, inflammation, stress, smoking, dehydration and medicines can temporarily change counts. | NHS — Blood testsnhs.ukSource-linked context |
| Blood cancer or marrow disorder missed | Important if persistent or marked | Persistent unexplained abnormalities, blasts, splenomegaly or symptoms need haematology review. | NHS — Blood testsnhs.ukSource-linked context |
| Clot or bleeding risk underestimated | Count- and cause-dependent | Very high red cells, platelets or very low platelets can have immediate management implications. | NHS — Blood testsnhs.ukSource-linked context |
| No trend available | Common limitation | Previous blood counts often clarify whether this is new, chronic, worsening or stable. | Guide sourcesClinical context |
These are literature figures, not a personalised prediction. Your own risks and likely benefits depend on your circumstances, your health, and how your care is carried out and followed up.
What happens afterwards
There is usually no physical recovery from blood tests, though you may have a short wait for results. If you need a bone marrow test, there may be some soreness for a few days. 'Afterwards' here mostly means understanding your results and knowing the next step.
- Minor bruising after a blood test
- A normal return to daily activities straight away
- Some soreness for a few days after a bone marrow test, if you have one
- A period of waiting for results, which can feel anxious
- Sometimes needing repeat tests before there is a clear answer
Aftercare
- Make sure you know how and when you will get each result, and who to contact with questions.
- Ask what each result means and what the next step is, including if it is normal or unclear.
- Keep a copy of your results, as trends over time are useful for future care.
- If a treatable cause is found, follow the advice given and attend any follow-up.
- If monitoring is advised, attend repeat blood tests as arranged.
- After a bone marrow test, follow the advice on the puncture site and report increasing pain, bleeding or signs of infection.
- Tell your doctor about any new or worsening symptoms while you wait for answers.
- Knowing which part of your blood count is abnormal and what is being checked
- A list of your medicines and supplements
- Any previous blood results to show trends
- A clear plan for how and when results will be given
- Knowing who to contact with questions or new symptoms
- Understanding the plan if a bone marrow test is suggested
- A copy of your results kept for future reference
⚠ Get urgent help if…
- Drenching night sweats, unexplained weight loss, or fevers without an obvious infection
- Unusual or easy bruising or bleeding, or many tiny red spots on the skin
- Repeated or severe infections
- New lumps, such as swollen glands in the neck, armpit or groin, that do not settle
- Severe tiredness, breathlessness or looking very pale
- Bone pain, or pain and fullness under the left ribs (an enlarged spleen)
- After a bone marrow test: increasing pain, bleeding that will not stop, or a fever (possible infection)
Who to contact: your clinician, clinic or test provider first (keep their number to hand). For urgent advice when you can't reach them, call NHS 111. In an emergency, call 999.
General guidance — it doesn't replace the specific advice your specialist gives you.
Results & realistic expectations
A good outcome from this investigation is a clear, safe explanation for the abnormal count. Often that is reassuring — a temporary or harmless cause, or a treatable one such as iron or vitamin deficiency. Sometimes it identifies a condition that needs monitoring or treatment, including, in a minority, a blood disorder or blood cancer.
A normal or improving result does not always rule out every condition, and a single abnormal result is not a diagnosis on its own — which is why trends and the whole picture matter. Some results take time, and a few are borderline or inconclusive and need monitoring. Ask your doctor what your specific results mean for you, and what would happen next under each possibility.
How long a result stays meaningful depends on the cause. A clearly explained, temporary change may need no further action. A borderline or unexplained result may be monitored with repeat tests over time, because trends reveal more than one snapshot. If a condition is diagnosed, ongoing follow-up is guided by that condition rather than by this initial work-up.
Related tests, treatments or support
An abnormal blood count is usually interpreted alongside your symptoms, examination and other tests, rather than in isolation. Related tests — a blood film, iron and vitamin levels, inflammation markers, kidney and liver tests, genetic tests, scans, or a bone marrow test — are combined as needed to build the full picture. Bringing previous results helps your doctor see how things are changing.
Follow-up & long-term care
Follow-up depends on what is found. You may be told a clear result and discharged, given treatment for a cause, asked to have repeat tests to watch a trend, or referred to a haematologist for further assessment. You should always know how you will get your results, what they mean, and who to contact with questions or new symptoms.
- Repeat blood tests over time if a result needs monitoring
- Keeping copies of results so trends can be tracked
- Following up any treatable cause that is found
- Reporting new or worsening symptoms while under investigation
- Ongoing follow-up guided by any condition that is diagnosed
Repeat, follow-on and what comes next
- Repeat or additional tests are common, because a single result rarely gives the full answer.
- Some results are borderline or inconclusive and need monitoring over time.
- A bone marrow test occasionally needs repeating if the first sample is inadequate.
- The plan can change as results come back, from reassurance to monitoring or treatment.
Ask what happens if the result is unclear or needs repeating, and what is included if further tests or follow-up are needed.
What good aftercare looks like
- A clear explanation of each result and the specific next step.
- A named contact and a defined route for getting results and asking questions.
- A sensible monitoring plan with repeat tests where a result is borderline.
- Specialist (haematology) interpretation of complex or worrying results.
- Results and the plan shared with your GP so your care stays joined up.
What affects the cost
Costs vary a great deal between people and providers, and we don't publish prices. What matters is understanding what drives the cost and making sure your quote is complete. The main things that affect it:
- The number and type of blood tests needed, including specialist or genetic tests
- Whether a blood film and laboratory review are required
- Any scans, such as an ultrasound
- A bone marrow test and its laboratory analysis, if needed
- Consultant haematologist time to interpret results and advise
- Follow-up appointments and any repeat (monitoring) tests over time
- Coordination with NHS records and any onward referral
- The consultant or clinician fee and who interprets your results
- The cost of each test, including any specialist or genetic tests
- Laboratory and reporting fees, including a blood film if needed
- The cost of a bone marrow test and its analysis, if it is required
- Follow-up appointments and any repeat monitoring tests
- How results are given and what happens if they are inconclusive
- How the investigation is coordinated with your NHS records and GP
On the NHS? Investigating an abnormal blood count is usually done on the NHS, often starting in general practice; private care is used mainly for speed of access, choice of consultant or a second opinion, and should be joined up with your NHS records.
You're entitled to your total cost in writing — including reports, follow-up and what happens if the result is inconclusive — before you decide.
Consent traps and marketing red flags
These are not small details. They are often where patients lose choice, time to reflect, or realistic expectations.
Consent traps
- Extensive or expensive tests done without explaining what they would change.
- Not explaining that a normal result does not rule out every condition.
- An abnormal result presented as a diagnosis before the work-up is complete.
- A bone marrow test suggested without explaining alternatives, discomfort and its small risks.
- No clear plan for how results are given, who interprets them, and what happens next.
Marketing red flags
- Promising that a private blood panel 'catches everything' or rules out cancer.
- Selling broad screening tests to healthy people without a clear reason.
- Jumping to expensive or invasive tests before simple steps such as a repeat count.
- Giving complex results without a haematologist to interpret them.
- No plan to join results up with your GP or NHS records.
Choosing a specialist safely
- Check the specialist is on the GMC Specialist Register for this area.
- Make sure they work at a CQC-registered service, and look for membership of the relevant Royal College or professional body.
- You're entitled to time to consider and to have your questions answered before you agree — the specialist who looks after you should explain it, not a salesperson.
- Be wary of pressure: time-limited offers or deposits taken before you've had time to think are red flags, not bargains.
- You're entitled to your total cost in writing — including any follow-up — before you decide.
Questions to ask your medical professional
Take this to your consultation. A good specialist will welcome every one of these.
- Which part of my blood count is abnormal, and what are the most likely causes?
- What will this test, or the next test, actually change for me?
- What happens if the result is normal, abnormal, or inconclusive?
- Do I need a repeat test or monitoring rather than an immediate answer?
- Will I need to see a haematologist, and would a bone marrow test ever be needed?
- How and when will I get my results, and who do I contact with questions?
- Are there symptoms that should prompt me to seek help sooner?
- Are you on the GMC Specialist Register for this area, and which Royal College or professional body are you a member of?
- Will you be the specialist who carries out my test, and who looks after me afterwards?
- What are the risks for someone like me, and how often do your own patients have a problem or need it repeated or redone?
- What does a realistic result look like — and what can this test not achieve?
- What are my options, including waiting, doing nothing for now, or choosing a different approach?
- Can I have written information, results and aftercare instructions in a format I can use, including any accessibility or communication support I need?
- What is the total cost in writing, including any follow-ups, and how much time do I have to decide?
Frequently asked questions
Does an abnormal blood count mean I have cancer?
Why do I need to repeat the blood test?
Will I definitely need a bone marrow test?
How long will it take to get answers?
Can I have this done privately to get answers faster?
What if the results are normal but I still feel unwell?
Is the bone marrow test very painful?
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How we made this page
Medically reviewed by a GMC-registered consultant. Written in plain English, checked against NHS, NICE, GMC and relevant Royal College / specialist-society guidance, and kept under review. No clinic paid to appear on this page, and we publish no pricing. This is general information to help you prepare — it is not a substitute for advice from your own clinician. How we review our guides →
Source hierarchy: UK regulator and NHS/NICE guidance first, then relevant Royal College or specialist-society guidance, then peer-reviewed evidence for procedure-specific figures where available.
Sources & standards: NHS — Blood tests Blood Cancer UK — Testing for essential thrombocythaemia NHS — Erythrocytosis (raised red cell count) British Society for Haematology — Guidelines
Reviews reflect patients' experience of care, not clinical outcomes. For procedure volumes and outcome data see PHIN.
Last medically reviewed 2026-09-21. Spotted something wrong or out of date? Report an error in this guide.
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