Concentration of Urine Samples Improves Sensitivity in Detection of Strongyloides -Specific IgG Antibody in Urine for Diagnosis of Strongyloidiasis

Abstract

Detection of IgG in urine is an efficient method comparable to that in serum for diagnosis of strongyloidiasis but effects of daily variation in urine dilution on diagnostic accuracy is not clearly known. This study evaluated effects of urine concentration on detection of parasite-specific IgG by urine enzyme-linked immunosorbent assay (ELISA), particularly in individuals with border-line results or false-negative diagnosis. Optimal concentration conditions were established by comparing Strongyloides -specific IgG antibody levels between unconcentrated and concentrated urine in participants with different infection intensities, namely healthy control (HC), low-negative (LN), high-negative (HN) and low-positive (LP) groups. The optimal condition was selected and validated in a field-trial study. The final urine concentration protocol required centrifugation at 4,000 g at 4°C for 10 mins using the Amicon® concentrator tube. This protocol was validated in groups of participants with varying diagnoses according to urine ELISA and fecal examination (n=148). The concentrated-urine ELISA increased the proportion of positive results in the LN group by 68.2% and by 100% in the HN group. Significantly elevated IgG antibody levels were seen in the LP group. In the group that was false negative by urine ELISA but positive by fecal examination (n=28), concentrated-urine ELISA yielded 100% positive results. Overall, the frequency estimates of S. stercoralis were 23.6% by fecal culture, 27% by standard urine ELISA and 90.5% by concentrated-urine ELISA. Concentration of urine samples prior to analysis by ELISA improved the sensitivity for diagnosis and is potentially useful in diagnosis of strongyloidiasis in immunocompromised individuals or in low-prevalence areas.

Epidemiology of strongyloidiasis determined by parasite-specific IgG detections by enzyme-linked immunosorbent assay on urine samples using Strongyloides stercoralis, S. ratti and recombinant protein (NIE) as antigens in Northeast Thailand

“…Similar observations have been reported in previous serum-based diagnostic studies and were believed to be associated with low immunity [ 44 ] or excessive dilution of urine samples [ 45 , 46 ]. Since urine composition is related to water intake, future work to concentrate urine samples prior to ELISA may help to alleviate the problem of false negative results [ 47 ]. Second, although analysis of urine and serum samples by ELISA had high concordance for qualitative and quantitative diagnosis of strongyloidiasis [ 22 , 24 , 47 ], this needs to be confirmed in different endemic settings.…”

“…Since urine composition is related to water intake, future work to concentrate urine samples prior to ELISA may help to alleviate the problem of false negative results [ 47 ]. Second, although analysis of urine and serum samples by ELISA had high concordance for qualitative and quantitative diagnosis of strongyloidiasis [ 22 , 24 , 47 ], this needs to be confirmed in different endemic settings. Third, additional confirmation other than parasitological, such as DNA detection by fecal PCR or immune-complex detection [ 48 , 49 ] in cases of false-positive urine ELISA is needed to better evaluate the performance of parasite-specific IgG detection in serum as well as in urine.…”

Diagnostic performance of a urine-based ELISA assay for the screening of human schistosomiasis japonica: A comparative study

“…The concentration of antibodies in urine is only about 1/4,000 to 10,000 of that in serum ( Nagaoka et al, 2021 ). Previously, it had been shown that the sensitivity of a urine-based ELISA was improved in the diagnosis of strongyloidiasis by adding a concentration protocol of urine samples ( Chungkanchana et al, 2022 ). In addition, the diagnostic accuracy of the POC-CCA methodology was significantly increased by introducing a phase of urine concentration in two Brazilian S. mansoni endemic areas ( Grenfell et al, 2018 ).…”

“…In contrast, urine-based diagnostic tests involve convenient and completely non-invasive urine sampling, with the limited chance of participants being exposed to biological risks. Previously, urine-based ELISA assays have been suggested as a possible alternative tool to diagnose a number of parasitic helminthiases such as echinococcosis, filariasis, opisthorchiasis, and schistosomiasis ( Itoh et al, 2001 , 2003 ; Sunita et al, 2007 ; Sawangsoda et al, 2012 ; Samad et al, 2013 ; Chirag et al, 2015 ; Eamudomkarn et al, 2018 ; Nagaoka et al, 2021 ; Chungkanchana et al, 2022 ). In this study, we aimed to validate a urine-based SjSAP4 + Sj23-LHD-ELISA assay for the diagnosis of S. japonicum infection in a human cohort recruited from areas in the Philippines moderately endemic for schistosomiasis japonica.…”