Serodiagnosis with a single quantification method suffers from high false positive/negative rates. In this study, a three-channel platform with an accessional instrumented system was constructed for simultaneous electrochemical, luminescent, and photothermal quantification of H2S, a bio-indicator for acute pancreatitis (AP) diagnosis. Utilizing the specific reaction between platform and H2S, the three-channel platform showed high sensitivity and selectivity in the biological H2S concentration range. The three-channel platform was also feasible for identifying the difference in the plasma H2S concentrations of AP and normal mice. More importantly, the precision of AP serodiagnosis was significantly improved (>99.0%) using the three-signal method based on the three-channel platform and an optimized threshold, which was clearly higher than that of the single- or two-signal methods (79.5%-94.1%). Our study highlights the importance of constructing a multichannel platform for the simultaneous multi-signal quantification of bio-indicators, and provides rigorous ways to improve the precision of medical serodiagnosis.