Abstract: The automated reader operates within an enclosure also containing a sample rack and reagent rack, as well as a microtiter plate with multiple wells therein. The machine automatically loads sample and reagent into a well of the microtiter plate according to a testing protocol. The specimen can then be moved along with the microtiter plate into a slot of the reader and aligned with either a light source and detector for an optical density read or aligned with a photon counter for a chemiluminescence read. The reader includes a shroud assembly which can be raised and lowered by a lift assembly to occlude a read point from photons other than those emanating from the sample.