Abstract: Compositions, methods, and functional immunoassays for measuring functioning of organs, receptors, and biological processes in a subject are provided. Functional immunoassay combines pharmacokinetics of xenobiotics after administering one or more of the compositions to a subject by quantifying the xenobiotic in samples taken from the subject. The method provides a xenobiotic that is processed principally by a single organ system with minimal metabolism and involves administering the xenobiotic to the subject, measuring its concentration in samples of biological material obtained over time, calculating a kinetic parameter that describes change in concentration over time, and associating this parameter with the functioning of the target organ. Functional immunoassay is used for measuring, for example, kidney, brain, lung, cardiovascular, gastrointestinal, and immune system function; progression of cancer and infectious disease; and diabetes and inflammatory disease status.

Abstract: Stable isotope labeling and neutron activation to measure biological functions are provided, as are the use and method of adding a chemical monitor to correct for neutron flux to sample vials prior to the addition of sample is presented, and the use of stable isotopes as a chemical bar code for vials and other items. Methods are provided also for measuring glomerular filtration rate and glomerular sieving function in a subject, and for measuring other physiological functions.

Abstract: Stable isotope labeling and neutron activation to measure biological functions are provided, as are the use and method of adding a chemical monitor to correct for neutron flux to sample vials prior to the addition of sample is presented, and the use of stable isotopes as a chemical bar code for vials and other items. Methods are provided also for measuring glomerular filtration rate and glomerular sieving function in a subject, and for measuring other physiological functions.