How do I request schistosomiasis IgG serology for an adult patient with recent freshwater exposure in an endemic area, intermittent abdominal pain, watery diarrhea, and peripheral eosinophilia?

How to Request Schistosomiasis Serology

Order schistosomiasis IgG serology through a specialist laboratory, as this is the primary screening test for your patient with freshwater exposure, abdominal symptoms, diarrhea, and eosinophilia. 1, 2

Specific Test to Order

• Request "Schistosoma antibody serology" or "Schistosoma IgG" from a specialist/reference laboratory – standard hospital laboratories typically do not perform this test. 1, 2

• Specify the clinical context on the requisition: recent freshwater exposure in endemic area, eosinophilia, and compatible symptoms to help the laboratory select appropriate antigens. 3

• Do not wait for stool microscopy results before ordering serology – concentrated stool microscopy has very low sensitivity and will miss most infections in this clinical scenario. 1, 2

Timing Considerations

• Serology becomes positive 4–8 weeks after exposure but may take up to 22 weeks in some cases. 1, 2

• If your patient's exposure was less than 4 weeks ago, serology may still be negative – consider repeating in 2–4 weeks if initial test is negative but clinical suspicion remains high. 1

• In acute Katayama syndrome (fever, urticarial rash, cough, eosinophilia 2–9 weeks post-exposure), serology may be negative early on – treat empirically and confirm with repeat serology later. 1, 4

Complementary Testing to Order Simultaneously

• Order concentrated stool microscopy on at least 3 separate specimens – while sensitivity is low, finding eggs confirms active infection and species identification. 1, 2

• Check complete blood count with differential – eosinophilia >0.45 × 10⁹/L strongly supports the diagnosis when combined with exposure history. 1

• Consider screening for Strongyloides serology as well – this coinfection is common in travelers/migrants and must be excluded before any corticosteroid use. 4

Interpretation Framework

• Positive serology + positive stool microscopy = confirmed intestinal schistosomiasis; treat immediately with praziquantel. 2

• Positive serology + negative stool microscopy = probable infection; treatment is justified on serology alone – do not delay therapy awaiting stool confirmation. 1, 2

• Negative serology with strong clinical suspicion (compatible exposure, symptoms, eosinophilia) = consider repeat serology in 2–4 weeks or proceed to colonoscopy with rectal biopsy. 2

Critical Pitfalls to Avoid

• Never use serology to assess treatment success – antibodies persist for years after cure and cannot distinguish active from past infection. 1, 2, 4

• Do not rely on single stool sample – egg excretion is intermittent and a single negative stool does not exclude infection. 1, 2

• Do not delay treatment in symptomatic patients with positive serology – waiting for microscopic confirmation increases risk of complications including hepatosplenic disease. 2

• Recognize that standard hospital labs cannot perform this test – you must specifically request referral to a specialist/reference laboratory that handles tropical disease serology. 1, 2

Geographic Context for Species Consideration

• Africa exposure (most common in UK/US): primarily S. mansoni and S. haematobium – if species unknown, treat with praziquantel 40 mg/kg single dose. 1, 2

• Asia-Pacific exposure: S. japonicum or S. mekongi – requires higher dose praziquantel 60 mg/kg divided into two doses. 1, 2

• When geographic history is unclear, default to the higher Asia-Pacific dosing regimen to ensure adequate treatment of potentially resistant species. 2