This technology includes device and sensor selection for the detection of blood metabolites which can be used to diagnose and monitor diseases in real-time. Currently the monitoring of metabolite levels is performed with specialized mass spectrometry instrumentation, therefore patient quality-of-life and financial advantages exist to develop devices capable of detecting metabolites in real-time. Our invention deals with the reduction to practice of this concept, showing how to select the metabolite and immobilized enzymes, how to do the immobilization, how to attach the components to the electrode, how to make the measurement and develop a prototype. Further, our invention deals with selection of light source and light detection to quantitate the blue color produced, as well as specific design features of the portable meter to enable direct loading of small volume of whole blood, transport of the sample through the fluidic channels and chambers, and mixing of the reagents.