A retaining clip retaining a plurality of reagent test slides in a stacked arrangement, the retaining clip (200, 300) comprising: - a middle plate (204, 304) having a first side and a second side opposite the first side; - a first cover plate (212, 310) joined to and slidable on the middle plate (204, 304) and extending transversely to and outwardly from the first side of the middle plate (204, 304); and - a second cover plate (202, 302), the second cover plate (202, 302) being joined to the middle plate (204, 304) and extending transversely to and outwardly from the first side of the middle plate (204, 304), the first cover plate (212, 312) and the second cover plate (202, 302) being in overlying relationship with each other to define therebetween a space for receiving the plurality of reagent test slides in a stacked arrangement; - wherein the middle plate is provided with a slot formed through the thickness thereof, and the first cover plate includes an extended portion having a T-shape and which extends through the slot of the middle plate and outwardly from the second side of the middle plate, the first cover plate being slidably coupled by the T-shaped extended portion to the middle plate so that the first cover plate is slidable on the middle plate; or - wherein the middle plate includes a T-shaped rail extending outwardly from the first side thereof and in a direction between the first cover plate and the second cover plate, the first cover plate including a main body portion, a first L-shaped leg extending co-planarly from the main body portion and a second L-shaped leg extending co-planarly from the main body portion and in the same direction as the first L-shaped leg, the first L-shaped leg and the second L-shaped leg being spaced apart from one another to define therebetween a T-shaped slot (344, 346) for receiving the T-shaped rail of the middle plate, wherein the clip retains a plurality of reagent test slides stacked between the first cover plate (212, 310) and the second cover plate (202, 302) and wherein each reagent test slide of the plurality of reagent test slides includes opposite lateral edges and a recess formed in each lateral edge, and wherein the width of the first cover plate (212, 310) and the width of the second cover plate (202, 302) are less than the width of each reagent test slide received and retained of the plurality of reagent test slides measured between the recesses formed in the lateral edges thereof so that the first and second cover plates (212, 310; 202, 302) do not overlie the recesses formed in the lateral edges of each reagent test slide of the plurality of reagent slides. - a middle plate (204, 304) having a first side and a second side opposite the first side; - a first cover plate (212, 310) joined to and slidable on the middle plate (204, 304) and extending transversely to and outwardly from the first side of the middle plate (204, 304); and - a second cover plate (202, 302), the second cover plate (202, 302) being joined to the middle plate (204, 304) and extending transversely to and outwardly from the first side of the middle plate (204, 304), the first cover plate (212, 312) and the second cover plate (202, 302) being in overlying relationship with each other to define therebetween a space for receiving the plurality of reagent test slides in a stacked arrangement; - wherein the middle plate is provided with a slot formed through the thickness thereof, and the first cover plate includes an extended portion having a T-shape and which extends through the slot of the middle plate and outwardly from the second side of the middle plate, the first cover plate being slidably coupled by the T-shaped extended portion to the middle plate so that the first cover plate is slidable on the middle plate; or - wherein the middle plate includes a T-shaped rail extending outwardly from the first side thereof and in a direction between the first cover plate and the second cover plate, the first cover plate including a main body portion, a first L-shaped leg extending co-planarly from the main body portion and a second L-shaped leg extending co-planarly from the main body portion and in the same direction as the first L-shaped leg, the first L-shaped leg and the second L-shaped leg being spaced apart from one another to define therebetween a T-shaped slot (344, 346) for receiving the T-shaped rail of the middle plate,