Immunoglobulin level testing (Quantitative immunoglobulins (serum IgG, IgA, IgM))
A blood test that measures the main antibody types — IgG, IgA and IgM — to look for an antibody deficiency or excess, usually when infections are frequent or severe or another condition is suspected.
✓ Medically reviewed by a GMC-registered consultant · last reviewed September 2026 · next review September 2027 · how we review
In short
- It measures how much IgG, IgA and IgM antibody you have — useful for spotting antibody deficiency or excess.
- It shows the amount of antibody, not how well it works, and does not check IgG subclasses, so a normal result does not rule everything out.
- Results often come back within days, but a low or high level usually needs repeating and interpreting alongside your history.
- An abnormal level is a clue, not a diagnosis — a clinical immunologist works out whether it is inherited, caused by another condition, or not significant.
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 detect an antibody deficiency that may explain recurrent or severe infections
It is the wrong first test if the concern is how well antibodies work rather than how much there is — a vaccine-response test is needed for that.
Blood is taken from a vein in a few minutes. No special preparation is usually needed.
A named clinician, ideally a consultant immunologist, responsible for interpreting results.
Blood is taken from a vein in a few minutes. No special preparation is usually needed.
Press on the site briefly. Mild bruising is normal. You can drive and work straight away.
Results are usually available. Your immunologist compares them with age-appropriate ranges.
A low or high level is often repeated, and low IgG may lead to IgG subclass or vaccine-response testing.
What is immunoglobulin level testing?
Immunoglobulins are antibodies — proteins your immune system makes to fight infection. This blood test measures the amount of the three main classes: IgG (the most common, giving long-term protection), IgA (which protects surfaces such as the gut and airways) and IgM (the first antibody made in a new infection).
The test is usually done when antibodies are too low, which can leave you prone to recurrent or severe infections, or too high, which can happen in infections, autoimmune conditions and some blood disorders. It is often one of the first tests a clinical immunologist arranges when an antibody problem is suspected.
This test measures how much antibody you have, but not how well it works. It also does not break IgG into its subclasses. So a normal result does not always rule out an antibody problem, and a low result is a starting point for further assessment rather than a final answer.
Low levels can be inherited (a primary immunodeficiency) or caused by something else — for example protein loss through the kidneys or gut, or certain medicines. Working out the cause is part of the specialist's job, not something the number reveals on its own.
Types, options & approaches
There may be different ways to do this. The right approach depends on the clinical question and your circumstances.
Options at a glance
These are the main approaches described in this guide. The right option depends on the diagnosis, your goals and what your clinician thinks is safe.
IgG
The main long-term protective antibody. Low IgG is the most important pattern when looking for antibody deficiency that may need treatment.
IgA
Protects mucosal surfaces such as the gut and airways. Selective IgA deficiency is common and often causes no symptoms at all.
IgM
The first antibody made when you meet a new infection. Levels can rise in recent infection and change in some immune conditions.
Serum electrophoresis / paraprotein check
When levels are high, the lab can check whether the increase is spread across many antibodies (polyclonal) or comes from one abnormal clone (monoclonal), which is...
Preparing for your test
- Bring a clear account of your infections: how often, how severe, any hospital admissions or unusual germs.
- List all your medicines and supplements; steroids and some other drugs lower antibody levels.
- Mention recent infections or vaccinations, which can temporarily change levels.
- Tell the team about any kidney problems, bowel disease or conditions causing protein loss.
- Share any family history of antibody deficiency or frequent serious infections.
- Bring previous results if you have them, to track changes and avoid repeating tests.
- No fasting is usually needed for this test, but check any specific instructions.
What happens
A nurse or phlebotomist takes a blood sample from a vein in your arm. It only takes a few minutes and you can carry on with your day straight away.
The laboratory measures the concentration of IgG, IgA and IgM. If a level is unexpectedly high, the lab may add further tests such as serum electrophoresis to see whether the rise is polyclonal or monoclonal. Results are then compared with age-appropriate reference ranges.
Your immunologist interprets the levels alongside your symptoms and history. A single abnormal result is often repeated, and low IgG in particular usually leads to further tests such as IgG subclasses or a vaccine-response check.
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…
- It is the wrong first test if the concern is how well antibodies work rather than how much there is — a vaccine-response test is needed for that.
- Testing during or just after an infection or vaccination can give misleading levels.
- On its own it cannot confirm a specific immunodeficiency diagnosis.
- If you are on steroids or immune-suppressing drugs, the result may reflect the medicine.
- It is not a useful 'general health' test for vague tiredness without an infection pattern.
Delay or rearrange if…
- You currently have an active infection or have just recovered from one.
- You have been vaccinated in the last few weeks.
- You are on steroids or other immune-affecting medicines not yet discussed with the team.
- A condition causing protein loss is being treated and levels may be temporarily distorted.
- Previous results are awaited that could avoid a repeat test.
Alternatives to discuss
- No test if there is no clear infection pattern and symptoms are mild.
- Addressing common causes first, such as iron deficiency or stress.
- A standard NHS pathway via your GP, who can arrange first-line tests and refer.
- Vaccine-response testing if the question is antibody function rather than amount.
- Specialist immunology review to decide what testing, if any, is warranted.
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.
Benefits
- Can detect an antibody deficiency that may explain recurrent or severe infections
- Can flag a raised antibody level that needs further investigation
- Helps guide whether you need vaccines, preventive antibiotics or specialist referral
- A clear normal result can be reassuring and reduce unnecessary further testing
- Forms a baseline that future results can be compared against
Risks & complications
- Minor bruising or soreness where blood was taken
- Borderline or mildly low results that need repeating
- Finding selective IgA deficiency that causes no symptoms but raises questions
- Anxiety while waiting for results
- Feeling faint during the blood test
- A raised level that triggers further tests for a blood disorder
- Difficulty interpreting a borderline result
- Infection at the needle site
- A misleading result that delays the right diagnosis if acted on without specialist input
The main pitfalls are interpretation, not the blood test itself. Levels vary with age, recent infection and medicines, so a single number can mislead. Low IgG matters most and usually needs further antibody-function testing; a raised level needs checking for whether it is polyclonal or monoclonal. Ask who will interpret the result and what the next step is.
Published figures to discuss
This is a low-risk blood test, so there are no surgical-style complication rates. The clinically important point is interpretation: levels vary with age, infection and medication, low IgA is often harmless, and a single abnormal result frequently needs repeating. Because meaningful figures depend heavily on the population and reason for testing, exact percentages are not quoted here.
| Figure | Reported range | How to interpret it | Source / confidence |
|---|---|---|---|
| Selective IgA deficiency | One of the commonest primary immune deficiencies; often quoted around 1 in 600 people of European ancestry | Many people are asymptomatic, but recurrent infections, gut disease or transfusion reactions may be relevant. | Newcastle Hospitals NHS — Clinical immunology and allergy referral guidelinesnewcastle-hospitals.nhs.ukPublished figure |
| Common variable immunodeficiency (CVID) | Rare; often quoted around 1 in 25,000 to 1 in 50,000 | Diagnosis requires low immunoglobulins plus clinical context and impaired antibody function, not IgG alone. | Newcastle Hospitals NHS — Clinical immunology and allergy referral guidelinesnewcastle-hospitals.nhs.ukPublished figure |
| Secondary hypogammaglobulinaemia | Common in immunology practice | Rituximab, haematological malignancy, nephrotic syndrome, protein-losing enteropathy and some medicines are key causes. | Guide sourcesClinical context |
| Infusion reaction if immunoglobulin replacement is started | Uncommon to common, usually mild; serious reactions are rare | Route, dose, rate, hydration and product choice are individualised. | 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 no physical recovery from having blood taken. 'Afterwards' is about waiting for the result and understanding what a low, high or normal level means for you.
- A small bruise or tender spot where blood was taken
- No change in how you feel — the test does not treat anything
- Being asked to repeat the test because levels vary
- A normal result even though symptoms continue
- Finding harmless selective IgA deficiency by chance
Aftercare
- Keep the dressing on for an hour or so if the site is sore.
- Note how and when you will receive your results.
- Do not start or change any medicines based on a result until a clinician advises.
- If a repeat or further test is recommended, arrange it promptly.
- Bring your infection history and questions to the results appointment.
- Keep a copy of your result to track changes and avoid duplicate testing.
- Ask whether a raised level needs any further checks.
- Infection timeline written down
- Medicine and supplement list ready
- Note of recent infections or vaccinations
- Previous immunoglobulin results gathered
- Family history of antibody problems noted
- Clear note of how results will be communicated
- Questions for the results discussion prepared
⚠ Get urgent help if…
- A high temperature with shivering, confusion or feeling very unwell — seek urgent help; do not wait for results
- A severe chest infection, breathing difficulty or chest pain
- An infection that is spreading or not responding to treatment
- Repeated serious bacterial infections such as pneumonia, sinus or ear infections
- Unexplained weight loss, night sweats or bone pain (which may need urgent assessment)
- Feeling faint or unwell after the blood test itself
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 normal set of immunoglobulin levels is reassuring but does not rule out every antibody problem, because the test does not measure how well antibodies work or check IgG subclasses. A low IgG, IgA or IgM is a meaningful starting point, but the cause still has to be worked out — it may be inherited, caused by another condition, or, in the case of isolated low IgA, often harmless.
A raised level is not a diagnosis either. It can reflect a recent infection, an autoimmune condition or, less commonly, a blood disorder, and the laboratory and immunologist decide which further tests are needed. The most useful result is one that changes your care — so it is fair to ask your specialist what each finding actually means for you.
Antibody levels change over time. They can fall with certain illnesses, protein loss or medicines, and rise temporarily after infection. Levels also differ with age, especially in children. A result is therefore a snapshot, and your immunologist may repeat the test if it was borderline, if your symptoms change, or to confirm a finding before acting on it.
Related tests, treatments or support
Immunoglobulin levels are often the first step, with IgG subclass testing and a vaccine-response check added when IgG is low or antibody function is in question. Complement and autoantibody tests may be done alongside if an autoimmune condition is being considered. A raised level may prompt serum electrophoresis to look for a paraprotein.
Follow-up & long-term care
If levels are normal and symptoms mild, no further action may be needed. A low IgG usually leads to further antibody-function testing and specialist referral. A raised or monoclonal result is investigated through the appropriate pathway. A good service makes clear who is responsible for explaining results and arranging the next step.
- Repeat testing if a result was borderline or your symptoms change
- Ongoing monitoring if an antibody deficiency is confirmed and treated
- Keeping vaccinations up to date as advised by your specialist
- Keeping your own record of results to track trends
Repeat, follow-on and what comes next
- A single abnormal level is commonly repeated before it is acted on.
- Low IgG usually leads on to further tests such as subclasses and vaccine-response testing.
- A normal level does not exclude an antibody-function problem.
- Levels change with infection, protein loss, medication and age.
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 named clinician, ideally a consultant immunologist, responsible for interpreting results.
- A clear timeline and route for receiving results, including borderline ones.
- A plan for repeating borderline results and for further antibody-function testing if IgG is low.
- Onward referral to a specialist immunology centre when a significant deficiency is found.
- Honest discussion if results are normal but symptoms persist.
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:
- Whether IgG, IgA and IgM are tested together or as part of a wider panel
- Additional laboratory tests if a level is raised (such as serum electrophoresis)
- The consultant immunologist's fee for interpreting results, not just the lab fee
- Whether further antibody-function testing is likely to be needed
- Phlebotomy and laboratory processing fees
- Any follow-up consultation to discuss results
- Which immunoglobulins are included and any add-on tests if levels are abnormal
- The laboratory fee and the consultant's interpretation fee, separately
- Whether a follow-up appointment to discuss results is included
- What it costs if the test needs repeating because a level is borderline
- Whether further tests (subclasses, vaccine response) are extra
- Who is responsible for explaining abnormal results and next steps
On the NHS? Immunoglobulin testing is available on the NHS when clinically indicated; private testing is sometimes used for faster access, but low or high results still require specialist interpretation and often further tests.
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
- Treating a single low or high number as a diagnosis without repeating or interpreting it.
- Not explaining that this test misses antibody-function problems and IgG subclass issues.
- Labelling harmless selective IgA deficiency as a significant problem.
- Not arranging the further tests that a low IgG usually requires.
- Not making clear who interprets the result and arranges follow-up.
Marketing red flags
- Selling immunoglobulin levels as a stand-alone 'immune health check' to well people.
- Implying a normal result proves a 'strong immune system'.
- Offering the test without specialist interpretation of abnormal results.
- Suggesting the test will explain general tiredness or frequent minor colds.
- Not mentioning that levels vary and may need repeating.
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.
- What will a low or high result change in my care?
- If my level is borderline, will you repeat the test, and when?
- Do any of my medicines or recent infections affect this result?
- If IgG is low, what further tests will I need?
- If a level is high, how will you check whether it is significant?
- Who will interpret the result and arrange any next steps?
- 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
Can I have this test on the NHS?
Does a normal result mean my immune system is fine?
I was told I have low IgA — should I worry?
What does a high immunoglobulin level mean?
Will I need more tests if my IgG is low?
Do my medicines affect the result?
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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: Lab Tests Online UK — Quantitative Immunoglobulins Immunodeficiency UK — Primary immunodeficiency information British Society for Immunology & UKPIN — immunoglobulin replacement therapy guideline British Society for Immunology — Clinical immunology guidelines Newcastle Hospitals NHS — Clinical immunology and allergy referral 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.
Related guides: Immune system blood tests · IgG subclass testing · Vaccine response testing · Complement testing · Autoantibody / autoimmune testing