A retaining clip for retaining reagent test slides in a stacked arrangement includes a first assembly having a first cover plate and at least two parallel, co-planar rails extending transversely from an inner surface of the first cover plate. A second assembly includes a second cover plate, and a rail receiving platform extending transversely from an inner surface of the second cover plate. The first cover plate and the second cover plate define between them a space for receiving the plurality of reagent test slides. The rails of the first assembly include ratchet teeth, and the rail receiving platform of the second assembly includes pawls. The pawls engage the ratchet teeth to prevent the separation of the first assembly and the second assembly and to securely but removably hold the plurality of reagent test slides in a stacked arrangement between the first and second cover plates.