Certain metabolic errors a person may be born with result in the alteration of the normal metabolism of one or more amino acids. Increased amino acid concentrations in blood plasma may also reflect inherited metabolic abnormalities. Blood plasma is the most informative way to check for most amino acid problems. Amino acid quantities in urine are also used to evaluate errors of metabolism. In most, but not all, cases where an amino acid is elevated in blood, it will also be elevated in urine. In general, urinary amino acid levels are much more variable than plasma levels. Blood plasma is the best way for an initial screen. The urine test checks for errors in amino acid metabolism that may lead to several diseases. Often, these diseases can be treated with proper diet and nutrition, as long as the disease has been identified. Quality of Life is often improved when patients are successfully identified and treated. These diseases are PKU (phenylketonuria), maple syrup urine disease, cystinuria, homocystinuria, Hartnup, arginonosuccinic aciduria, histidinemia, hyperpolinemia type A, and citrullinuria. This urine test checks for the following amino acids: (alanine, ethanolamine group); (argininosuccinic acid, histidine, arginine, lysine, ornithine, cystathionine, cystine, cysteine, hydroxylysine group); (homocitrulline, glycine, serine, hydroxyproline, aspartic acid, glutamine, citrulline group); (homocystine, asparagine group); (leucine, isoleucine group); phenylalanine; proline; (threonine, glutamic acid group); (tryptophan, -amino isobutyric acid group); tyrosine; (valine, methionine group