Assessment of the suitability of the dried blood spot (DBS) samples for detection of Treponemal antibodies using <i>in vitro</i> assays

Background & objectives This study was performed to assess the suitability of dried blood spot (DBS) samples for the serological screening of syphilis. Methods Two hundred paired DBS and plasma samples collected from six sexually transmitted infection (STI) clinics during the year 2023 were tested using three kits -Treponema pallidum haemagglutination assay (TPHA), Syphilis Total Ab and ErbaLisa Syphilis after standardization of the dilutions of the DBS elutes and considering the results of the paired plasma samples as a true status. Results The TPHA showed 89 per cent sensitivity and 100 per cent specificity, the EIA-Syphilis Total Ab. Kit showed 100 per cent sensitivity and 97 per cent specificity, whereas ErbaLisa syphilis showed 89 per cent sensitivity and 100 per cent specificity. However, one kit Syphilis ELISA (Oscar Medicare Pvt. Ltd., New Delhi) did not show agreement with the paired plasma samples at any dilution and was not considered suitable for the testing of DBS samples. The agreement between the plasma and DBS results was found to range from 94.5 to 98.5 per cent with a kappa agreement score of 0.89 for TPHA, ErbaLisa, and 0.97 for ELISA-Syphilis Total Ab. Interpretation & conclusions The findings of this study confirmed that the DBS samples can be used for the detection of anti-treponemal antibodies using the above-validated kits and thus may be a valuable tool in surveillance and epidemiological surveys conducted in India. The study also highlighted the need for validation of any plasma/serum syphilis antibody detection assay on DBS samples before using it on DBS samples.