Short answer
Strongyloides stercoralis is a parasite that can persist for years. Stool exams can miss it because larvae may be shed intermittently and in low numbers. Serology, often called Strongyloides antibody testing, is commonly used when chronic infection is suspected, especially before steroids or other immunosuppression in someone with exposure risk.
Test differences
| Test | What it can show | Limit |
|---|---|---|
| Strongyloides IgG antibody | Evidence of current or past infection/exposure. | May not distinguish active from past infection and can cross-react. |
| Stool O&P or larvae exam | Can directly detect larvae. | Single stool exams have limited sensitivity. |
| CBC with eosinophils | May show eosinophilia. | Eosinophils can be normal, especially in severe hyperinfection. |
When each test fits
Serology is often favored when chronic infection is suspected or when stool exams are negative but exposure risk is meaningful. Stool testing is more direct but can miss infection because larvae are shed intermittently. CBC eosinophils can add context but should not be used alone to rule Strongyloides in or out.
Why a negative stool test may not settle it
Strongyloides larvae may be sparse, so a single stool exam can miss infection. CDC guidance emphasizes that serial stool examination is the diagnostic standard, and serology may still be needed when suspicion remains.
What a positive antibody can and cannot say
A positive antibody supports exposure and possible infection, but it does not prove the infection is active right now or tell you whether larvae are still being shed. Cross-reactivity and slow titer decline can complicate interpretation after treatment.
Why it can be high-stakes
Strongyloides can become life-threatening during corticosteroid therapy or other immune suppression. People with past residence or travel in endemic areas, unexplained eosinophilia, compatible symptoms, or upcoming immunosuppression should discuss testing and treatment with a clinician.
Questions to ask
- Does my travel, birthplace, military service, barefoot soil exposure, or prior sanitation exposure create risk?
- Should antibody testing be used instead of, or in addition to, stool testing?
- Am I about to start steroids, chemotherapy, transplant medicines, or biologic therapy?
- If antibody is positive, what treatment and follow-up are recommended?
FAQ
Why is stool testing alone often not enough?
Larvae can be shed intermittently, so one stool sample may miss infection even when Strongyloides is present.
When is antibody testing more useful?
Serology is often useful when chronic infection is suspected or when stool exams are negative but exposure risk is real.
Can a positive antibody mean a past infection?
Yes. Antibodies may persist after treatment or past exposure, so the result needs clinical context.
Why is Strongyloides high-stakes before steroids?
Immunosuppression can trigger hyperinfection or disseminated disease, which can be severe or fatal.
Should eosinophils be used alone?
No. Eosinophils can be helpful context, but normal counts do not rule Strongyloides out.
Who should interpret the result?
A clinician can decide whether stool exams, serology, treatment, or infectious disease input is the safest next step.
Related guides: stool ova and parasite test, enteric parasite PCR panels, CBC blood test, and Entamoeba histolytica stool test.