(In the absence of secretion, creatinine behaves like inulin). Ketoacids, cimetidine, and trimethoprim reduce creatinine tubular secretion and, therefore, increase the accuracy of the GFR estimate, in particular in severe kidney dysfunction. In cases of severe kidney dysfunction, though, the CrCl rate will overestimate the GFR because hypersecretion of creatinine by the proximal tubules will account for a larger fraction of the total creatinine cleared. The GFR is clinically important as a measurement of kidney function. Blood creatinine concentrations may also be used alone to calculate the estimated GFR (eGFR). Therefore, creatinine concentrations in blood and urine may be used to calculate the creatinine clearance (CrCl), which correlates approximately with the glomerular filtration rate (GFR). If the filtration in the kidney is deficient, blood creatinine concentrations rise. Little or no tubular reabsorption of creatinine occurs. Ĭreatinine is removed from the blood chiefly by the kidneys, primarily by glomerular filtration, but also by proximal tubular secretion. Creatine conversion to phosphocreatine is catalyzed by creatine kinase spontaneous formation of creatinine occurs during the reaction. It is then transported through blood to the other organs, muscle, and brain, where, through phosphorylation, it becomes the high-energy compound phosphocreatine. Creatinine itself is produced via a biological system involving creatine, phosphocreatine (also known as creatine phosphate), and adenosine triphosphate (ATP, the body's immediate energy supply).Ĭreatine is synthesized primarily in the liver from the methylation of glycocyamine (guanidino acetate, synthesized in the kidney from the amino acids arginine and glycine) by S-adenosyl methionine. Serum creatinine (a blood measurement) is an important indicator of kidney health, because it is an easily measured byproduct of muscle metabolism that is excreted unchanged by the kidneys. It is released at a constant rate by the body (depending on muscle mass). Creatinine ( / k r i ˈ æ t ɪ n ɪ n, - n iː n/ from Ancient Greek: κρέας (kréas) 'flesh') is a breakdown product of creatine phosphate from muscle and protein metabolism.
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