Device and method for obtaining clinically significant analyte ratios

A method for determining the concentration of an analyte in a sample of body fluid which comprises the steps of:

• a) providing a test matrix in the form of a strip through which the fluid sample can flow by capillarity, said strip having a first region which contains mobile specific binding partner for the analyte which binding partner bears a visually detectable label and can react with the analyte to form an analyte/labeled binding partner complex, at least one second region which contains immobilized analyte or an immobilized binding partner which is specific for an epitope of the analyte different than that to which the labeled binding partner is specific, at least one third region which contains means for capturing the analyte/labeled specific binding partner complex which is not bound in the second region and a fourth region which contains means for calorimetrically producing a visually detectable signal the intensity of which corresponds to the level of a second analyte in the sample of body fluid whose concentration is clinically related to that of the first analyte whose concentration is being determined;
• b) developing the matrix by applying a sample of a body fluid suspected of containing the first and second analytes thereto thereby allowing it to contact the labeled specific binding partner so that analyte present in the fluid sample binds to the labeled specific binding partner to form a complex while leaving excess, unreacted labeled binding partner free to further react whereby the fluid sample carries the analyte/labeled binding partner complex and unreacted labeled binding partner along the matrix by capillarity to the second region containing the immobilized analyte in which region unreacted labeled binding partner is bound to the immobilized analyte in inverse relationship to the concentration of the first analyte in the fluid tests sample or the analyte/labeled specific binding partner complex is bound to the immobilized specific binding partner in a direct relationship to the concentration of first analyte in the fluid test sample;
• and the labeled specific binding partner which did not bind to the second region is carried by capillarity to the third region where it is immobilized by the immobilization means;
• c) reading the second region of the developed matrix on a reflectance meter having a detector capable of measuring the visible signal from the visually detectable label to determine the concentration of the visually labeled binding partner in the second zone and reading the third zone of the developed strip in a similar manner to determine a signal from the labeled binding partner in the third zone of the matrix;
• d) determining the final response signal by ratioing the signals from the labeled binding partner captured in the second region and the labeled binding partner immobilized in the third region;
• e) determining the concentration of the first analyte in the fluid sample by comparing the final response signal determined in step d with final response signals determined in a similar manner for fluid samples containing known concentrations of the first analyte;
• and
• f) correcting the concentration of the first analyte as determined in step e by determining the concentration of the second analyte in the fluid test sample by measuring the intensity of the signal in the fourth region of the strip using a reflectance meter and then determining the ratio of the second analyte to the first analyte whose quantitative concentration is being sought.