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Giardiasis Diagnosis
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Giardiasis
Diagnosis

Diagnostic methods

Parasitological diagnosis
Giardia cysts and trophozoites can be detected in faecal samples. Since Giardia is not regularly found in the stools, multiple samples have to be analysed.
As a supplement, duodenal samples can be analysed (in aspirates or using the “Entero-Test”).

Molecular diagnosis
Real-time PCR or nested PCR amplifying the small subunit ribosomal RNA gene to detect and quantify G. lamblia trophozoites. The detection limit for the rt-PCR is 50 trophozoites per gram stool.

Antigen detection
Several commercially available test kits detect with a high sensitivity Giardia copro-antigens in faecal samples by immunochromatographic, immunoenzyme or direct fluorescent antibody assays.

Antibody detection

Not of diagnostic relevance since it cannot distinguish past from acute infection.

 

Diagnostic strategies

  1. To confirm a Giardiasis infection
    If one has to rely on microscopy, at least three independent stool samples should be screened before one rules out the diagnosis! As an alternative strategy, one could use an antigen detection assay analysing one sample. If the test result is negative a second sample should be screened.
     
  2. To screen patients with diarrhoea for protozoa infections
    At least three stool samples should be taken. Microscopic analyses allow detection of several pathogens. This may also be realized using a multiple antigen detection assay (e.g. Triage Micro Parasite assay). In the near future, a multiplex rt-PCR might be the optimized method, depending on its validation.
     
  3. For epidemiological studies
    For convenience one may rely on antigen detection, avoiding laborious microscopy.
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