Parasitic infection assessment (Investigation for intestinal and tissue parasites)
Tests, usually on stool and blood, to find out whether symptoms such as tummy upset, an itchy bottom, or an unexplained raised blood count are caused by a parasite.
✓ Medically reviewed by a GMC-registered consultant · last reviewed September 2026 · next review September 2027 · how we review
In short
- It uses stool, blood and sometimes urine tests to find out whether a parasite is causing your symptoms.
- Several stool samples on different days are usually needed, and one negative result does not always rule a parasite out.
- A raised eosinophil blood count can be a clue, but many parasites do not raise it - a normal count is not reassurance on its own.
- Do not self-treat with worming or antiparasitic medicines; the right treatment depends on the exact parasite, and some need specialist care.
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.
Finds out whether a parasite is causing your symptoms
Empirical self-treatment with worming or antiparasitic medicines is not a substitute for identifying the parasite.
You collect stool samples on different days as instructed, and have blood (and sometimes urine) tests. This staggered approach improves accuracy.
Clear instructions for collecting the right number of samples and a route to get all results.
You collect stool samples on different days as instructed, and have blood (and sometimes urine) tests. This...
Stool microscopy and blood-count results usually return within days. The clinician explains whether a parasite was...
Specific antibody tests, often sent to reference laboratories, can take longer; you are told when and how you will...
If a parasite is found, you are given the specific treatment for it. Some are a single dose; others need a short...
What is a parasitic infection assessment?
A parasitic infection assessment is a set of tests to find out whether a parasite is causing your symptoms. Parasites are organisms that live in or on the body; the ones that matter here range from common gut worms to those caught abroad through food, water, soil or freshwater swimming.
The assessment usually starts with your history - symptoms, travel, where you have lived, food and water, and freshwater exposure - and an examination. The main tests are stool samples examined under the microscope for the eggs (ova), cysts and bodies of parasites, often blood tests, and sometimes a urine sample for certain parasites such as those causing schistosomiasis.
A key point is timing and numbers: because parasites are shed on and off, at least three stool samples on different days are usually recommended, and even then a single negative result does not always exclude infection. Blood tests may show a raised count of a cell called the eosinophil, which can be a clue to certain parasites - but many parasitic infections do not raise it, so a normal count does not rule them out either.
The assessment cannot treat the parasite; its job is to find out whether one is present and which it is, so that the correct, specific treatment can be given. Because some parasitic infections are uncommon in the UK and others can be dangerous if treated wrongly, this is an area where specialist input is often valuable.
Types, options & approaches
There may be different ways to do this. The right approach depends on the clinical question and your circumstances.
What stool tests and the eosinophil count can and cannot tell you
| Test | Good at | Limitation |
|---|---|---|
| Stool microscopy | Finding gut parasites | Misses on-and-off shedding |
| Eosinophil count | Hinting at some parasites | Often normal in infection |
| Specific serology | Strongyloides, schistosomiasis | Can stay positive after cure |
| Urine test | Some schistosomiasis | Timing of sample matters |
No single test is perfect. A normal eosinophil count or one negative stool sample does not exclude a parasite, which is why several tests and, where relevant, specialist input are used together.
Preparing for your test
- Note your symptoms, when they started, and any travel or time living abroad, including rural stays.
- Mention freshwater swimming, the food and water you had, and contact with soil or animals.
- Expect to collect more than one stool sample on different days, following the instructions given.
- Tell the clinician about all medicines, especially any worming or antiparasitic treatments already tried.
- Crucially, mention if you take, or are about to start, steroids or any medicine that weakens the immune system, as this affects which parasites must be excluded first.
- Bring details of previous test results, including any done abroad or privately.
What happens
The clinician asks about your symptoms, travel and exposures, and examines you. You are usually given containers and instructions to collect several stool samples on different days, because parasites are shed intermittently. Blood is often taken, including a full blood count to look at the eosinophil level and, where relevant, specific antibody tests. A urine sample may be requested for certain parasites.
The samples are examined in the laboratory - stool under the microscope for eggs, cysts and parasites, and blood for the relevant tests. Some results come back within days; specialist antibody tests, often sent to reference laboratories, can take longer.
You go home the same day. If a parasite is found, you are offered the specific treatment for it; if the picture is unclear, the clinician explains whether to repeat tests, seek specialist input, or look for another cause. Where there is an unexplained raised eosinophil count, especially with relevant travel, a structured set of tests is followed.
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…
- Empirical self-treatment with worming or antiparasitic medicines is not a substitute for identifying the parasite.
- Relying on a single stool sample or a normal eosinophil count to exclude infection is unsafe.
- Routine testing is the wrong response if you are acutely unwell - that needs urgent assessment.
- Non-specialist testing may be inadequate for uncommon or tropical parasites that need reference-laboratory tests.
Delay or rearrange if…
- You are acutely unwell and need urgent assessment before routine sample collection.
- Samples cannot yet be collected and handled correctly to give reliable results.
- You are about to start steroids or immune-suppressing treatment - strongyloides should be considered first, which may change the order of testing.
- Recent antiparasitic treatment could affect results and needs to be taken into account.
Alternatives to discuss
- No testing, with watchful waiting and safety-netting, when symptoms are mild and there is no concerning exposure.
- Targeted treatment for a clearly identified, common parasite such as threadworm.
- Referral to a tropical-medicine or infection specialist for complex or uncommon parasites.
- Investigating other, non-parasitic causes when the picture does not fit a parasite.
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
- Finds out whether a parasite is causing your symptoms
- Identifies which parasite, so the correct treatment can be given
- Helps explain an unexplained raised eosinophil blood count
- Can detect important infections, such as strongyloides, before immune-suppressing treatment
- Avoids unnecessary or wrong antiparasitic treatment when no parasite is present
Risks & complications
- The inconvenience of collecting several stool samples over different days
- Brief discomfort or bruising from blood tests
- A single negative result that does not fully exclude a parasite, so tests may be repeated
- Waiting for specialist antibody results that take longer
- A false-negative result leading to a missed or delayed diagnosis
- A normal eosinophil count giving false reassurance when a parasite is in fact present
- Needing referral to a specialist or reference laboratory for less common parasites
- A false-positive antibody result suggesting a parasite that is not actually present
- Anxiety from an incidental or hard-to-interpret finding
- Serious harm from starting immune-suppressing treatment (such as steroids) before strongyloides has been excluded, which can trigger overwhelming infection
The main pitfalls are testing once when several samples are needed, and assuming a normal eosinophil count rules out infection - it does not. A particularly important safety point is strongyloides: this parasite can persist quietly for years and can become overwhelming and life-threatening if steroids or other immune-suppressing treatments are given without it being excluded first. If you may need such treatment, make sure this is considered.
Published figures to discuss
The accuracy of parasite tests depends on the parasite, the timing and number of samples, and the test used. Stool microscopy can miss infections that are shed intermittently, which is why several samples are advised. Eosinophil count is an unreliable screen on its own because many helminth infections do not raise it. Antibody tests can stay positive after successful treatment. We have not given exact accuracy percentages here because they vary so much by parasite and method, and over-precise figures could mislead.
| Figure | Reported range | How to interpret it | Source / confidence |
|---|---|---|---|
| Stool microscopy misses intermittent shedding | Recognised limitation | Several stool samples on different days may be needed, and some parasites require serology or PCR rather than stool microscopy alone. | Guide sourcesClinical context |
| Normal eosinophil count falsely reassuring | Common limitation | Eosinophilia is a clue for some helminths but can be absent; it is not a reliable screen for all parasites. | Guide sourcesClinical context |
| Empirical treatment before diagnosis | Condition-dependent risk | Some drugs can be harmful or inadequate if the parasite is wrong, and strongyloides matters before steroids or immunosuppression. | UK guidelines for the investigation and management of eosinophilia in returning travellers and migrants (Journal of Infection, 2024)journalofinfection.comSource-linked context |
| Chronic complications if missed | Parasite-specific | Schistosomiasis, strongyloidiasis and some tapeworm infections can persist for years and need targeted follow-up. | UK guidelines for the investigation and management of eosinophilia in returning travellers and migrants (Journal of Infection, 2024)journalofinfection.comSource-linked 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 the tests themselves. What matters afterwards is interpreting the results correctly, completing any specific treatment, and arranging follow-up where needed.
- Collecting several samples over a few days before results are complete
- Waiting longer for specialist antibody results
- Being asked to repeat stool tests if the first set was negative
- Mild side effects from antiparasitic treatment if a parasite is treated
- Symptoms settling gradually after the correct treatment
Aftercare
- Follow the instructions for collecting and returning samples carefully, including the number and timing.
- If a parasite is found and treated, take the treatment exactly as prescribed and complete any course.
- Practise good hand hygiene, especially for gut parasites, to avoid passing infection to others.
- For threadworm and some other infections, follow advice about treating household members and washing bedding and clothing.
- Attend any repeat or follow-up tests, particularly if the first results were negative but symptoms continue.
- Do not start immune-suppressing treatment such as steroids without checking whether strongyloides needs excluding first.
- Report side effects of treatment rather than stopping it yourself.
- Seek further assessment if symptoms persist, worsen, or new ones develop.
- Sample containers and clear collection instructions
- A note of travel, exposures and symptom timing
- Details of any antiparasitic medicines already tried
- A reminder to mention any planned steroid or immune-suppressing treatment
- A clear way to get all your results, including specialist ones
- Advice on treating household members where relevant
- Contact details and a plan for follow-up or repeat testing
⚠ Get urgent help if…
- A high fever, feeling very unwell, or rapidly worsening symptoms - seek urgent assessment.
- Severe or bloody diarrhoea, persistent vomiting, or signs of dehydration.
- Severe tummy pain, or a swollen, tender abdomen.
- Breathlessness, a persistent cough, or wheeze (some parasites move through the lungs).
- New confusion, severe headache, fits, or weakness.
- Becoming acutely unwell soon after starting steroids or immune-suppressing treatment, especially if strongyloides was not excluded (seek urgent help).
- A severe allergic reaction to treatment - rash, facial or lip swelling, or difficulty breathing (call 999).
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
If a parasite's eggs, cysts or body are seen in a sample, or a specific antibody test is positive, that identifies the cause and points to the right treatment. Because parasites are shed intermittently, a negative stool result - especially a single one - does not exclude infection, so several samples or repeat testing may be needed. A normal eosinophil blood count is reassuring but does not rule out a parasite, as many do not raise it.
Results need careful interpretation: some antibody tests can stay positive long after successful treatment, and a positive test is not always proof of active infection. The assessment tells you whether and which parasite is present so treatment can be targeted; it cannot, by itself, guarantee that every possible parasite has been excluded.
Once a parasite is correctly identified and treated, most infections clear, though some need a follow-up test to confirm cure. A few parasites, such as strongyloides, can persist quietly for many years if not treated, which is why exposure history matters even long after travel. Treatment does not make you immune, so future exposure - for example on further travel or freshwater swimming - can lead to new infection.
Related tests, treatments or support
Parasite testing is frequently part of a wider assessment after travel or for an unexplained raised eosinophil count, alongside tropical disease diagnosis and treatment and screening for other infections. Specialist tropical-medicine units coordinate stool, blood and urine tests, and reference-laboratory tests, so that the right combination is chosen and interpreted together.
Follow-up & long-term care
Follow-up depends on the result. If a parasite is treated, a check or repeat test may confirm it has cleared. If the first tests were negative but symptoms continue, repeat or additional testing, or specialist referral, is arranged. Where a raised eosinophil count remains unexplained, structured follow-up is recommended. Your GP and any specialist are kept informed.
Repeat, follow-on and what comes next
- A negative stool result often needs repeating, with several samples on different days.
- An unexplained raised eosinophil count may need a structured set of further tests over time.
- A positive antibody test may need careful interpretation, as it can persist after cure.
- Some parasites require a follow-up test to confirm that treatment has worked.
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
- Clear instructions for collecting the right number of samples and a route to get all results.
- Correct, specific treatment if a parasite is found, with advice on completing it and treating contacts where relevant.
- Consideration of strongyloides before any immune-suppressing treatment.
- A plan for repeat testing, follow-up or specialist referral if results are negative 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 you see a GP or a specialist, and the length of the appointment
- The number and type of tests (multiple stool samples, blood tests, urine, serology)
- Whether specialist or reference-laboratory tests are required
- How quickly results are processed and reported
- Any treatment needed if a parasite is found
- Follow-up or repeat testing to confirm cure or clarify an uncertain result
- The consultation fee and how long the appointment lasts
- Which tests are included, the number of samples, and the laboratory fees
- The cost of specialist or reference-laboratory tests
- Who interprets the results and whether a written summary is included
- The cost of any treatment and follow-up testing
- What happens, and what it costs, if results are inconclusive or further tests are needed
On the NHS? Parasite testing is available on the NHS, with specialist tests accessed through reference laboratories; private testing exists but results need careful, expert interpretation.
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
- Not being told that one negative stool sample or a normal eosinophil count does not exclude a parasite.
- Starting steroids or immune-suppressing treatment without considering strongyloides.
- Treating empirically without identifying the parasite, risking the wrong or ineffective treatment.
- No clear plan for repeat testing, specialist input, or interpreting uncertain results.
Marketing red flags
- 'Comprehensive parasite cleanse' or 'detox' programmes that claim to clear all parasites.
- Selling antiparasitic 'kits' for self-treatment without diagnosis.
- Stool or blood 'parasite panels' marketed for vague symptoms without expert interpretation.
- Reassurance, or alarm, based on a single result without regard to test limitations.
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.
- Based on my travel and symptoms, which parasites are you testing for?
- How many samples do I need to give, and over how many days?
- Does my eosinophil count, or a negative stool test, actually rule anything in or out?
- Should strongyloides be excluded before I have any steroids or immune-suppressing treatment?
- If the tests are negative but I still have symptoms, what is the next step?
- 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
Why do I need to give more than one stool sample?
My blood count was normal - does that mean I don't have a parasite?
Can I just take a worming tablet to be safe?
Why are you asking about steroids or immune-suppressing medicines?
Is this testing available on the NHS?
How soon will I get my results?
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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: UK guidelines for the investigation and management of eosinophilia in returning travellers and migrants (Journal of Infection, 2024) Faecal ova, cyst and parasite (OCP) test - North West London Pathology (NHS) Parasite investigations - Gloucestershire Hospitals NHS Gastrointestinal worms and parasites - NHS Lothian RefHelp NHS - Threadworms
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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