A portable, electrically-powered instrument, intended to be used to scan an immunoassay reagent vehicle (e.g., test strip, cassette, or card) after exposure to a clinical specimen, to provide a quantitative, semi-quantitative and/or qualitative in vitro determination of chemical substances and/or biological markers in a clinical specimen. The instrument uses photometry to detect visual markers that result from the immunological reaction between the reagents and the specimen. It is intended to be used by health professionals for rapid in vitro diagnostic measurements at the point-of-care or in the laboratory.