In this work, we developed a measurement system that uses LEDs to estimate multiple components such as urea and creatinine in spot urine samples using near-infrared spectroscopy, considering future transition to LED light sources. In this study, we chose LEDs with 10 standard wavelengths (1400-2300 nm, in 100 nm increments). A multiple regression analysis using all combinations of 10 wavelengths was performed. We prepared glucose-added urine samples (GAU, urine samples from 10 healthy adults, each mixed with glucose). Wavelength selection was performed by comparing the minimum standard error of prediction (SEP, calculated from actual concentration and predicted concentration) for each wavelength combination. We obtained high accuracy for estimating urinary urea and creatinine levels (SEP: 42.4 mg/dl and 7.34 mg/dl, respectively) using four wavelengths for urea including two wavelengths showing negative absorbance, and ve wavelengths for creatinine. Furthermore, an extremely high correlation coef cient (γ > 0.99) was obtained for both components. We calculated urea concentration, creatinine concentration, and urea-to-creatinine ratio using this optical, reagentless method. The low SEP and high γ show that our method is suitable for practical determination of urea-to-creatinine ratio. Thus, this method of analyzing urine samples using NIR spectroscopy can be used to assess protein intake in CKD patients.

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Monitoring core body temperature (CBT) allows observation of heat stress and thermal comfort in various environments. By introducing a Peltier element, we improved the zero-heat-flux core body thermometer for hot environments. In this study, we performed a theoretical analysis, designed a prototype probe, and evaluated its performance through simulator experiments with human subjects. The finite element analysis shows that our design can reduce the influence of external temperature variations by as much as 1%. In the simulator experiment, the prototype probe could measure deep temperatures within an error of less than 0.1 °C, regardless of outside temperature change. In the ergometer experiment with four subjects, the average difference between the prototype probe and a commercial zero-heat-flux probe was +0.1 °C, with a 95% LOA of −0.23 °C to +0.21 °C . In the dome sauna test, the results measured in six of the seven subjects exhibited the same trend as the reference temperature. These results show that the newly developed probe with the Peltier module can measure CBT accurately, even when the ambient temperature is higher than CBT up to 42 °C.

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