1. A diagnostic test system, comprising: a housing comprising a port for receiving a test strip that supports lateral flow of a fluid sample along a lateral flow direction and comprises a labeling zone containing a labeling substance that binds a label to a target analyte and a detection zone comprising at least one test region containing an immobilized substance that binds the target analyte, wherein the detection zone includes an area that is exposed for optical inspection and is characterized by a first dimension transverse to the lateral flow direction and a second dimension parallel to the lateral flow direction; a reader that obtains separable light intensity measurements from each of multiple localized regions of the exposed area of the detection zone when the test strip is loaded in the port, wherein each of the multiple localized regions is characterized by at least one surface dimension smaller than the first dimension, wherein the reader comprises: a light source that scans a light beam to illuminate each of the multiple localized regions of the exposed area of the detection zone; and a light detector that has a field of view that encompasses the path of the light beam across the exposed area of the detection zone; and a data analyzer comprising software that identifies ones of the light intensity measurements obtained from the at least one test region and to compute at least one parameter from the identified ones of the light intensity measurements.