The sensitivity of sLHCGR and LH-sLHCGR ELISAs. The purity of the affinity purified recombinant LHCGR protein extracellular domain (a, indicated by an arrow) and LH-sLHCGR (d, indicated by arrows) proteins were examined in SDS-polyacrylamide gels-stained with coomassie blue. The small arrows above the major band in d) are either glycosylated or dimers because these bands react with anti-FLAG and LHR29 monoclonal antibodies. The sensitivity of the ELISAs was verified by linear responses to the dilution effect of sLHCGR (b) and LH-sLHCGR protein calibrators (e). The sensitivities of these assays were further examined by assaying serially diluted serum samples from three patients with known concentration of sLHCGR (c) and LH-LHCGR (f). Each data point in b and e represents mean value obtained from six independent dilution of the standards.