An apparatus for spectroscopic evaluation of a subject's body fluids may be used at the interstitial region adjacent to or in between a subject's extremities using a spectroscopic probe. The spectroscopic probe may possess one or more of the movements such as rotational, translational, and/or vertical freedom necessary for the probe to contact the subject's tissue at a consistent angle and pressure while accommodating the different size of the subject's extremities, and may be housed in a device optimized for attaining reproducible blood flow to the region of the subject that is measured, and for minimizing the effects of the housing pulling, stretching, pressing, compressing the subject's skin. A pressure sensor may be used to ensure that measurements are taken at an optimal pressure. A touch sensor may be used to activate a system and/or to ensure flushness. In addition, the spectroscopic measurement may be coupled with a temperature measurement means that detects the subject's local body temperature in or near the region being measured, or the subject's core or mean body temperature, or the ambient temperature proximate to the probe, or any combination of those measurements. The system may also include one or more indicators to communicate information to a test subject.