Patent ID: 7214542

Claim:
A method of testing a fluid sample to determine whether or not it contains a certain substance, comprising: using an assay test device having sample and reaction sensors mounted within a housing; storing a predetermined threshold range for readings of the sample and reaction sensors indicative of a desired amount of light within the housing prior to introduction of the fluid sample; using the sample sensor to determine an initial sample sensor reading; using the reaction sensor to determine an initial reaction sensor reading; storing the initial readings of the sample and reaction sensors; comparing the initial sample sensor reading to the predetermined threshold range; determining in response to the comparing the initial sample sensor reading to the predetermined threshold range whether or not the initial sample sensor reading is acceptable; comparing the initial reaction sensor reading to the predetermined threshold range; determining in response to the comparing the initial reaction sensor reading to the predetermined threshold range whether or not the initial reaction sensor reading is acceptable; generating a signal in response to either determining step finding an unacceptable initial reading to alert the user that the test device is faulty; flowing the fluid sample along an elongated test strip; using the sample sensor spaced from the test strip to detect the presence of the fluid sample using the light reflecting from a first location on the test strip; starting a timer for a predetermined time delay interval in response to the sample sensor detecting the fluid sample under test being received at the first location on the test strip; generating an electric time-out signal at the end of the predetermined time delay interval started by the sample sensor; using the reaction sensor remote from the sample sensor starting the time delay interval for detecting the fluid sample under test at a second location on the test strip in response to the time-out signal at the end of the time delay interval started by the sample sensor; determining whether or not the fluid sample under test at the second location on the test strip contains a predetermined quantity of the certain substance in response to the reaction sensor detecting the fluid sample under test; generating an electric output signal in response to the determination in the reaction sensor; and indicating the presence or absence of a predetermined quantity of the certain substance contained within the fluid sample under test, wherein the sample sensor and the reaction sensor are photo-optic sensors.