A fluidic device for mixing a reagent fluid with a fluid sample comprises a supply channel having a reagent inlet, a sample inlet and a first reagent storage, coupled to the supply channel; a mixer for mixing the reagent with the fluid sample, having a mixer inlet coupled to the supply channel at a position in between the sample inlet and the first reagent storage; In a first stage, when the reagent fluid is supplied in the reagent inlet, the reagent is provided in the supply channel and the first reagent storage, and such that the reagent is thereafter stationed in the supply channel and the first reagent storage until a fluid sample is provided in the sample inlet. When the fluid sample is supplied in the sample inlet, the supplied fluid sample and the stationed reagent flows into the mixer thereby mixing both fluids.