The present invention relates to a readhead for a photometric diagnostic instrument, such as a reflectance spectroscope, for performing tests on a sample of body fluid to be analyzed.
It is useful for various medical diagnostic purposes to utilize a reflectance spectroscope to analyze samples of body fluid, for example, to detect on immunotest strips or chemistry test strips the presence of blood in a person's urine. Conventional reflectance spectroscopes have been used to detect the presence of blood in a urine sample disposed on a reagent pad. Any blood present in the urine reacts with the reagent on the reagent pad, causing the reagent pad to change color to an extent which depends on the concentration of the blood. For example, in the presence of a relatively large concentration of blood, such a reagent pad may change in color from yellow to dark green.
One conventional reflectance spectroscope detects the concentration of the blood by illuminating the reagent pad and detecting, via a conventional reflectance detector, the amount of light received from the reagent pad, which is related to the color of the reagent pad. Based upon the magnitude of the reflectance signal generated by the reflectance detector, the spectroscope assigns the urine sample to one of a number of categories, e.g. a first category corresponding to no blood, a second category corresponding to a small blood concentration, a third category corresponding to a medium blood concentration, and a fourth category corresponding to a large blood concentration.
A prior art reflectance spectroscope has been provided with an optical system in the form of a read head in which a light bulb is disposed directly above the reagent pad to be tested and a reflectance detector is disposed at a 45.degree. angle to the horizontal surface of the reagent pad. Light from that spectroscope passes through a first vertical optical path from the illumination source to the reagent pad and through a second optical path, disposed 45.degree. with respect to the first optical path, from the reagent pad to the reflectance detector.
Other devices have been designed to illuminate a reagent pad. For example, U.S. Pat. No. 4,755,058 to Shaffer discloses a device for illuminating a surface and detecting the intensity of light emitted from the surface. The surface is directly illuminated by a plurality of light-emitting diodes disposed at an acute angle relative to the surface. U.S. Pat. No. 5,518,689 to Dosmann, et al. discloses a diffused light reflectance readhead in which one or more light-emitting diodes are used to illuminate a reagent pad and in which light from the reagent pad is detected by a light sensor.