Non-protein nitrogen

Non-protein nitrogen (NPN) compounds in plasma refer to a variety of nitrogen-containing substances in addition to various proteins. It includes urea, uric acid, creatine, amino acids, peptides, nucleotides, ammonia and so on. Urea content is the highest, followed by amino acids, uric acid, and creatinine. Since most non-protein nitrogen compounds are intermediate products of various protein metabolisms, they are more important than plasma proteins in determining protein breakdown. At present, the non-protein nitrogen compounds commonly measured in clinical practice are urea, creatinine, uric acid, amino acids and ammonia. It is mainly used for the evaluation of renal function, liver function, nucleic acid metabolism and nutritional status.