The Search Continues—An Ideal Marker of GFR

Abstract

The glomerular filtration rate (GFR) is generally considered the best measure of renal function despite the fact that the kidney performs an array of duties, including salt and water balance, erythropoiesis, bone metabolism, electrolyte homeostasis, and blood pressure control. GFR is traditionally measured as the renal clearance of a particular substance from plasma and is expressed as the volume of plasma that can be completely cleared of that substance in a unit of time. The ideal marker for GFR determinations would appear endogenously in the plasma at a constant rate, be freely filtered at the glomerulus, be neither reabsorbed nor secreted by the renal tubule, and undergo no extrarenal elimination. Although the ideal marker for measuring GFR has yet to be found, these characteristics can be useful benchmarks for comparing the advantages and disadvantages of new methods for GFR quantification. Measurement of urea marked the beginning of efforts to quantify renal function with its isolation by Rouelle in 1773 (1). Subsequently, Strauss introduced blood urea as a diagnostic test for renal disease in 1903. The concept of clearance as a measure of renal function followed in 1929 (2) and was subsequently extended to creatinine in the early 1930s (1). Blood urea nitrogen (BUN) concentration is generally recognized to …