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Investigations

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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Laboratory investigations:

microscopic examination for schistosome eggs - should be carried out at least two months after the last known fresh water contact
- in stools
  - by observing even a single egg in thick smears of stool specimens (2-10 mg) with or without suspension in saline
  - as many as three specimens may be needed to make a diagnosis in some patients
  - rapid, simple, and inexpensive Kato-Katz thick smear stool examination
    - recommended by WHO for intestinal schistosomiasis when the intensity of infection is high
    - requires 40-50 mg of faeces
    - has specificity of 100% but its sensitivity varies with prevalence and intensity of infection, as well as with the number of stool specimens collected and slides prepared for microscopy.
- in urine
  - S haematobium eggs can be detected on microscopy in a urine sample concentrated by sedimentation, centrifugation, or filtration and forced over a paper or nitrocellulose filter
  - urine should ideally be collected when there is maximum excretion of eggs - between 10am-2pm
PCR based assays for detection of schistosome DNA in faeces or sera and plasma
biopsy of bladder or rectal mucosa - may be useful for diagnosis in patients with a typical clinical presentation of schistosomiasis in the absence of eggs in urine or faeces
serological assays
- detects antibodies against schistosomal antigens
- most techniques detect IgG, IgM, or IgE against soluble worm antigen or soluble egg antigen by enzyme-linked immunosorbent assay (ELISA), indirect haemagglutination, or immunofluorescence.
- useful for symptomatic travellers, but for people in endemic regions serology cannot differentiate between active infection and past exposure
- positive test may be diagnostic in patients who are not excreting eggs e,g - Katayama syndrome
additional supportive laboratory evidence of schistosomiasis include:
- eosinophilia (>80% of the patients) with acute infections
- anaemia and thrombocytopenia - in chronic and advanced disease
- increased prothrombin time is indicated by an increased INR - may be seen in chronic and advanced disease
- hypoalbuminaemia
- raised concentrations of urea and creatinine
- hypergammaglobulinaemia and hypoalbuminaemia - in chronic and advanced disease (1,2)

Radiology

chest radiography
- pulmonary infiltrates can be seen in acute cases (Katayama syndrome)
abdominal ultrasound
- can establish extent of liver and spleen pathology in intestinal schistosomiasis
pelvic ultrasound
- useful in urinary schistosomiasis to identify the extent of bladder, ureteral and renal pathology (1,2)

Additional investigations:

cystoscopy - reveals characteristic "sandy patches" (1)
abdominal X-ray - bladder calcification
intravenous urogram - may demonstrate hydro-ureter, hydronephrosis or filling defects in the bladder

Reference:

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