A readhead for a photometric diagnostic instrument includes a housing adapted for incorporation within the photometric diagnostic instrument, and an elongated sample table operatively engaged with the housing. The sample table is configured to support elongated reagent sample media of the type having a plurality of test areas disposed in spaced relation thereon, each of the test areas being configured to react with a sample and to change color according to an amount of a constituent or property in the sample. A light source is provided to illuminate the sample table. An imager having an elongated field of view is coupled to the housing, the elongated field of view including at least a portion of the sample table. A scanning mechanism is configured to move the field of view relative to the sample table.