A device for detecting and/or quantifying functional C1-esterase inhibitor (fC1-INH), the device comprising: (i) a conjugate pad comprising a first zone and a second zone, on which a first agent and a second agent are immobilized, respectively, and (ii) a membrane, which is in communication with the conjugate pad, wherein the membrane comprises a third zone, on which a third agent is immobilized. The conjugate pad may further comprise a fourth zone for placing a biological sample, which flows through the device in the order of the first zone, the second zone, and the third zone.

The invention relates to the diagnosis of multisystem inflammatory syndrome (MIS) following exposure to an infectious agent, to monitoring the efficacy of therapy against MIS, to a method for predicting the risk of developing MIS and to biological agents for use in the therapy of MIS associated with an exposure to an infectious agent.