A non-invasive estimate of glomerular filtration rate derived from nonequilibrium thermodynamics

"nAcute kidney injury is characterised by elevated serum creatinine and reduced urine output, both of which reflect reduced glomerular filtration rate (GFR). The estimation of GFR is usually obtained from an empirical expression based on the serum creatinine concentration, although other analytes are also used. The selection of the ‘best' analyte and expression has been the subject of much debate. The thermodynamic foundation of GFR leads to an expression for GFR in terms of urine volume and osmotic potential, both of which are easily and non-invasively measured. This expression is consistent with at least some of the data in the literature and provides insight into some of the apparent inconsistency in the relationship between GFR and urine volume. While more complete data are required to evaluate it thoroughly, the expression complements the analyte-based methods for estimating GFR.