Can a Blood Test Detect Parasites?

Sometimes. A blood test can detect some parasites, but there is no single blood test that checks for all of them: according to the CDC, each blood test looks for one specific parasite infection. For the common intestinal worms, a stool test or a pinworm tape test is usually how the diagnosis is made, and a blood test mostly adds clues.

This page explains the kinds of blood tests used for parasites, what a high eosinophil count can and can't tell you, which worms a blood test can and can't find, and how blood tests fit alongside stool tests. It is general education, not medical advice.

The two kinds of blood tests for parasites

The CDC describes two general kinds of blood tests a clinician may order when a parasite is suspected:

• Serology (antibody or antigen tests). A blood sample goes to a lab, which looks for antibodies your immune system made against a particular parasite, or for pieces of the parasite itself (antigens). The clinician has to name which parasite to test for, because each serology test is specific to one infection.
• Blood smear. A drop of blood is placed on a slide, stained and looked at under a microscope. This finds parasites that live in the blood itself. The CDC gives malaria, babesiosis and filariasis as examples.

Most intestinal worms live in the gut, not the bloodstream, so a blood smear usually won't show them. That is the main reason a general "parasite blood test" doesn't exist.

What a high eosinophil count means

Many people first hear about parasites because a routine blood count came back with high eosinophils. Eosinophils are a type of white blood cell. MedlinePlus explains that they become active with certain allergic diseases, infections (including parasites) and other medical conditions, and that a normal absolute eosinophil count is under 500 cells per microliter. Ranges vary a little from lab to lab.

A raised count is a clue, not a diagnosis:

• It can point toward worms. The CDC Yellow Book notes that a raised eosinophil count is often what prompts clinicians to consider a parasitic infection, especially in someone returning from travel abroad.
• It has many other causes. Allergies, asthma, eczema, reactions to medicines, autoimmune conditions and some blood disorders can raise eosinophils too.
• A normal count doesn't rule worms out. The Yellow Book says eosinophilia is "not a perfect metric", and that other infections or medicines can keep the count down. People who have lived for years where a worm is common may have little or no rise.
• The number doesn't measure severity. The Yellow Book notes that the absolute eosinophil count does not predict how serious an infection is.

If your count is high, your clinician will usually ask about travel, symptoms, diet, skin contact with soil and your medicines before deciding which test, if any, comes next.

Which worms a blood test can and can't find

Blood tests are useful for some worms and not used at all for others:

• Pinworm: no blood test. The CDC states plainly that there are no blood tests to diagnose pinworm. Clinicians use the pinworm tape test instead, because the eggs are laid on the skin around the anus rather than in the blood or stool.
• Strongyloides: blood test often used. This is the main worm where a blood test matters. The CDC notes that ordinary stool exams often miss Strongyloides, so clinicians commonly order an antibody blood test. The CDC also points out the limits: some antibody tests cross-react with other worms, antibodies can stay positive after an infection is gone, and a significant share of people become antibody-negative within six months after successful treatment. See strongyloidiasis symptoms and treatment.
• Roundworm, hookworm and whipworm: mostly stool tests. These are usually diagnosed by finding eggs in a stool sample. A blood count may show raised eosinophils, especially early on while roundworm or hookworm larvae are passing through the body. See roundworm, hookworm and whipworm in humans.
• River blindness (onchocerciasis): usually a skin test. It is most often confirmed by checking a very thin skin sample under a microscope. See onchocerciasis (river blindness).

Blood test vs stool test

For most intestinal worms, a stool test is the main test, and a blood test plays a supporting role:

• A stool test looks for the worm or its eggs. The CDC recommends examining three or more stool samples collected on different days, because a single sample can miss parasites. Our guide to the stool test for parasites explains how that test is done and what the results mean.
• A blood test looks for your body's response, or for one named parasite. It can help when stool tests are negative but the history still points to a worm.
• Timing matters. The Yellow Book explains that eosinophils can rise early in an infection, while larvae are still moving through the body and before adult worms are laying eggs. At that stage a stool test can come back negative even though a worm is present. With Strongyloides, stool tests are commonly negative and serology is needed.

That is why a clinician may order both, and may repeat a test that comes back negative when the suspicion is strong. The CDC notes that labs throughout the United States can diagnose parasitic infections, and that a provider may have more than one lab look at a sample.

Can you order a parasite blood test yourself?

Some labs sell tests directly to consumers, but a parasite blood test only answers the question it was ordered for. Without knowing your symptoms and travel history, it is hard to pick the right test, and easy to misread a positive antibody result from an old infection or a negative result from an infection that is too early to show.

A clinician can decide which test fits, whether a stool test or tape test makes more sense, and what the results mean for you. If you're not sure where to start, our guide to what kind of doctor treats parasites explains when a primary care provider is enough and when a specialist helps.

Get in-person care promptly if you have a fever after travel abroad, blood in your stool, severe or worsening belly pain, signs of dehydration, a spreading rash, eye pain or vision changes, or a weakened immune system.

Getting a prescription through Get It Prescribed

Get It Prescribed is a telehealth service for adults. A licensed provider reviews a written health assessment, including any test results you already have, and decides whether mebendazole or ivermectin is appropriate for a labeled use. Mebendazole's labeled uses are pinworm, whipworm, roundworm and hookworm; ivermectin's are intestinal strongyloidiasis and onchocerciasis. Get It Prescribed does not treat malaria or other blood parasites. No prescription is guaranteed, and the provider may recommend testing or an in-person visit instead. How it works shows each step.

The medicines dispensed through Get It Prescribed are compounded preparations made by a licensed compounding pharmacy. They are not FDA-approved, the FDA has not reviewed them for safety, effectiveness or quality, and they are not generics of, or substitutes for, the brand-name products.

The cost is a one-time $50 provider consultation fee, plus $3.00 per ivermectin tablet or $3.50 per mebendazole capsule if a prescription is issued, with the quantity decided by the provider. The service is available in all 50 states and the District of Columbia; some states require a live phone or video visit.

This article is general education, not medical advice. It does not replace an evaluation by a licensed clinician who knows your history.

Related questions

Is there one blood test for all parasites?

No. The CDC says blood tests look for a specific parasite infection, and there is no blood test that looks for all parasitic infections. Your clinician chooses the test based on your symptoms, other health conditions and travel history.

Does a CBC show parasites?

Not directly. A complete blood count (CBC) with a differential reports your eosinophils, and a raised count can be a clue to a worm infection. But many other conditions raise eosinophils, and a normal count doesn't rule a parasite out.

Can a blood test detect worms in the intestine?

Only for some worms. An antibody blood test is commonly used for Strongyloides. Pinworm has no blood test, and roundworm, hookworm and whipworm are usually found with a stool test.

What level of eosinophils suggests parasites?

MedlinePlus lists a normal absolute eosinophil count as under 500 cells per microliter. A count above that has many possible causes, parasites among them, so the number alone can't confirm or rule out a worm. Your clinician reads it alongside your history.

Can a parasite antibody test be positive after treatment?

Yes. The CDC notes that antibodies can persist for some time, so it can be hard to tell an active infection from an older one. A significant share of people become antibody-negative within six months after successful treatment for Strongyloides.

Sources

• CDC: Diagnosis of Parasitic Diseases — serology and blood smears, why no blood test looks for all parasites, and stool exams on several samples.
• CDC: Clinical Overview of Strongyloides — stool exam limits, serologic tests, cross-reactions and antibodies after treatment.
• CDC: About Strongyloides — diagnosis with a blood test or a stool sample.
• CDC: Clinical Overview of Pinworm Infection — no blood tests to diagnose pinworm; the tape test.
• CDC Yellow Book: Post-Travel Parasitic Disease Including Evaluation of Eosinophilia — what eosinophilia can and can't show, and why stool tests can be negative early.
• MedlinePlus: Eosinophil count - absolute — what the test measures and the normal range.
• MedlinePlus: Complete Blood Count (CBC) — what a CBC with differential reports.
• MedlinePlus: Ova and Parasite Test — the stool test used for most intestinal worms.
• DailyMed: mebendazole chewable tablet prescribing information — labeled uses: pinworm, whipworm, roundworm and hookworm.
• DailyMed: ivermectin tablet prescribing information — labeled uses: intestinal strongyloidiasis and onchocerciasis.
• FDA: Compounding and the FDA — Questions and Answers — what compounded preparations are and how they are regulated.