The ornamental design for a reagentstrip, as shown and described.
FIG. 1 is a perspective view of a reagent strip showing the new design;
FIG. 2 is another perspective view thereof;
FIG. 3, FIG. 4, FIG. 5, and FIG. 6 are side views thereof;
FIG. 7 is a top view thereof; and,
FIG. 8 is a bottom view thereof.
The broken lines, the areas within them, and the unshaded areas bounded by both broken and solid lines depict portions of the reagent strip that form no part of the claimed design.