Abstract: Disclosed is an improved electrochemical sensor for the detection of an analyte in a fluid test sample. The electrochemical sensor is of the type in which the fluid test sample is drawn into a capillary space and the improvement to the sensor involves an arrangement where a portion of the sensor's counter electrode is placed on the edge of the capillary space in a relationship to the sensor's working electrode such that if the capillary space is not completely filled there will be generated only a very weak current. When the sensor is connected to a properly programmed current detector, the weak current caused by the underfilling of the capillary space will be detected as an error and will notify the user of the sensor that the test should not be continued.

Abstract: Disclosed is an improved electrochemical sensor having a base bearing a working and counter electrode which provides a flow path for a fluid test sample. The working electrode has a reaction layer on its surface which contains an enzyme capable of reacting with an analyte to produce electrons which are received by the working electrode. The base is mated with a cover to form a capillary space into which the test fluid is drawn. The improvement involves configuring the working and counter electrodes so that a major portion of the counter electrode is located downstream on the flow path from the working electrode with the exception of a small sub-element of the counter electrode which is in electrical communication with the primary portion of the counter electrode and located upstream of the working electrode.