What is the role of stool antigen detection in the diagnosis of giardiasis?

Updated: Oct 01, 2018
  • Author: Hisham Nazer, MBBCh, FRCP, DTM&H; Chief Editor: Burt Cagir, MD, FACS  more...
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Answer

Several tests to detect Giardia antigen in the stool are commercially available. [15, 37, 57] These utilize either an immunofluorescent antibody (IFA) assay or a capture enzyme-linked immunosorbent assay (ELISA) against cyst or trophozoite antigens. These tests have a sensitivity of 85-98% and a specificity of 90-100%.

Polymerase chain reaction (PCR) techniques may detect giardia in stool samples with parasites concentrations as low as 10 parasites/100 mcL. PCR may also be a valuable tool for screening of water supplies. [58] Real-time PCR has also the advantage of being able to detect both mild and asymptomatic infections. [59]

While more sensitive than stool examination, these examinations are limited to the detection of Giardia; isolated use might result in missing an alternative or concurrent parasitic infection.

A 2009 study evaluated a screening test for Giardia and Cryptosporidium on 136 fecal samples. The results showed the test to be 98.4% sensitive and 100% specific; the positive and negative predictive values were 98.7% and 99.3%, respectively. [60]


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