Sensitivity of microscopy versus enzyme immunoassay in the laboratory diagnosis of giardiasis

The substitution of enzyme immunoassay (EIA) techniques for microscopy as a screening tool forGiardia lamblia infection was assessed. Paired stool samples obtained within a ten-day period from 366 patients with persistent diarrhea were examined by microscopy. In addition, two commercially availableGiardia lamblia-specific ElAs were performed. Compared with microscopy, EIA for coproantigen detection was more sensitive, based on examination of either one or two stool samples. Repeated examinations increased the number of cases detected, more so for microscopy than EIA. The negative predictive values of the two EIAs performed on the first stool sample were 98.7% and 97.8%. The results show that EIA for detection of copro-antigens in a single stool sample may be almost as sensitive for identifyingGiardia infection as repeated microscopy on two sequential stool samples.