Features of determining relationships in aqueous biological solutions between biophysical constants and environmental parameters using optical methods

The relevance of early diagnostics of chronic kidney disease (CKD) is due to it high prevalence and asymptomatic course of the disease in the early stage. There is a need to develop new approaches to the diagnosis of early-stage kidney damage that are accessible, non-invasive and reliable, with an emphasis on the use of optical methods. A new method of rapid diagnosis based on refractometric measurement of the refractive index of urine has been proposed. New relationships between the refractive index, osmolality O_s, and density ρ have been established. Based on the values of O_s and ρ, doctors determine the presence of kidney disease or damage at an early stage (the patient is then referred for clinical examination). The proposed method provides high accuracy (the refractive index measurement error of ±0.5 in a wide temperature range of 288−303 K made it possible to determine O_s and ρ based on these measurements with an error of 2 mOsm/l and 0.15 g/cm³, which is sufficient to determine kidney damage at an early stage. This makes it competitive when compared to traditional methods of rapid kidney function testing (urinalysis, test strips, and mobile density meters). The results obtained for the diagnosis of kidney function were clinically confirmed during the examination of patients. This confirms the possibility of using refractometry for rapid diagnosis of kidney condition to detect damage at an early stage.