Abstract: An apparatus and method for measuring a bodily constituent such as glucose or cholesterol by analyzing a sample taken from the body such as blood, saliva or urine. The sample is placed on a test strip inserted into the test block portion of the apparatus where the portion of the sample containing the constituent desired to be measured reacts with a chemical reagent. Products of this reaction have an absorbance/reflectance characteristic which is mathematically related to the concentration of the constituent in the bodily sample. The reflected light is absorbed by a photodiode and the output of the photodiode converted to a digital form where a microprocessor can calculate the concentration of the constituent using the mathematical relationship between the reflected light and concentration stored in memory means of the apparatus.