Several manufacturers offer semi-automated instruments (dipstick readers) for reading reagent strips. Use of an instrument removes the subjectivity of visually interpreting color changes on reagent strips and ensures that tests will be read at the correct time. Transcription errors can also be avoided if the instrument is interfaced with the laboratory information system.
The technology employed is based on the principle of reflectance, with the amount of light reflected being inversely related to the concentration of substances present. An example of reflectance is the light that is scattered after light strikes an unpolished surface. Since each component on the dipstick produces a different color reaction, the light source for each test must be at the appropriate wavelength. This is accomplished either by using filters or monochromatic light sources. The percent reflectance is determined by dividing the test reflectance by the calibration reflectance and multiplying by 100. Algorithms are used to change the results obtained into a linear relationship with concentration of analyte.
