The assay device includes a first housing and a specimen holder rotatably fit in the first housing. The specimen holder has a center portion, a circular flange surrounding the center portion and a pin member extending from the underneath of the center portion. The center portion has a radial slot extending from its peripheral toward its center. A spring/latch assembly is adapted to be held in the slot on the specimen holder and includes a spring member disposed near the center of the center portion and a latch member having a remote end. The assay device also includes a second housing, preferably a cam plate fixedly fit in the first housing. The cam plate has a rim portion surrounding a concave portion adapted to accommodate the center portion of the specimen holder and an opening on the rim portion for adding a specimen to be tested. A plurality of cam-shaped chambers are provided in the rim portion and communicate with the concave portion. Each cam-shaped chamber has an apex portion located furthest away from the concave portion and a cam side extending from the apex portion toward the next chamber and each chamber has a capsule, retained therein, containing either a reagent or wash solution. When the specimen holder is rotated relative to the cam plate, the remote end of the latch member moves along the rim portion and thrusts into each chamber and breaks the capsule retained therein to release a reagent for testing an analyte(s) in a specimen.