Laboratory diagnosis for Giardia lamblia infection: A comparison of microscopy, coprodiagnosis and serology

Abstract

Objective: To evaluate newer techniques such as copro-antigen detection and serology in the diagnosis of symptomatic Giardia lamblia infection. Design: Blinded comparison of copro-antigen detection (by ELISA), serology (immunoglobulin IgG and IgM anti-G. lamblia by ELISA, and IgG, IgM and IgA by immunoblot) and microscopy in clinical samples. Microscopic findings for three preserved stools were considered the gold standard. Setting: Travel medicine clinic. Population studied: Adults, post-travel, with gastrointestinal symptomatology. Main results: For 152 previously collected stools, copro-antigen detection had a sensitivity of 73 of 74 (98.6%) and a specificity of 78 of 78 (100%). In clinical samples of 62 patients, eight of the 62 patients (13%) were diagnosed with G. lamblia infection on microscopy. Copro-antigen diagnosis was accurate in symptomatic patients, with sensitivity of seven of eight (87.5%) and specificity of 52 of 54 (96.8%). Serology was less accurate. IgG response to G. lamblia had sensitivity of four of seven and specificity of 24 of 50 (48%), and IgM response had sensitivity of three of six and specificity 27 of 48 (56%). Western blot had a sensitivity of five of seven and a specificity of 38 of 49 (78%). Conclusions: Copro-antigen diagnosis of G. lamblia is highly accurate in patients with chronic gastrointestinal complaints, while serology is less accurate and appears to be less useful diagnostically.