Amino Acid Analysis
When performing general screening for amino acid disorders, it is best to test both blood and urine. A decrease, or mild elevation, of amino acids can only be detected in blood. Conversely, accumulation of amino acids with very low renal threshold as well
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E. SHIH
• Specimens When performing general screening for amino acid disorders, it is best to test both blood and urine. A decrease, or mild elevation, of amino acids can only be detected in blood. Conversely, accumulation of amino acids with very low renal threshold as well as the renal transport defects will be evident in the urine. The significance of a renal aminoaciduria is very different from that of an overflow aminoaciduria from blood. For instance, large increases in urine cystine, arginine, lysine and ornithine of renal origin are diagnostic of cystinuria. On the other hand, a similar urine pattern can be associated with three other metabolic diseases, in which there are elevations of plasma arginine, lysine or ornithine, respectively. In contrast to metabolic defects of biogenic amine neurotransmitters, rarely is cerebrospinal fluid (CSF) preferred over blood and urine for diagnosis. It is often used to provide additional information, for confirmation of a diagnosis and to assess the degree of brain involvement. Vitreous fluid can be valuable in the post-mortem diagnosis of metabolic disorders when urine is often not available and blood is unsuitable due to post-mortem changes. Amino acid concentrations in vitreous fluid are in approximately the same range as found in plasma, except for glutamic acid, proline and glycine which are only one-tenth that in plasma. Amniotic fluid has limited value in prenatal diagnosis for the amino acidopathies. Unlike the organic acid disorders, in most amino acid disorders the metabolites do not accumulate before birth. Abnormal amino acid patterns in amniotic fluid have only been found in two of the urea cycle disorders, namely argininosuccinate lyase deficiency (argininosuccinic acidemia) and argininosuccinate synthetase deficiency (citrullinemia). Tables B.l-BA list the amino acid values in blood, urine, CSF and vitreous fluid and are included as a guideline. However, it should be noted that even when using the same instrumentation the reference values may vary from laboratory to laboratory. Most often, each laboratory establishes its own reference ranges.
N. Blau et al. (eds.), Physician’s Guide to the Laboratory Diagnosis of Metabolic Diseases © Springer-Verlag Berlin Heidelberg 2003
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Amino Acid Analysis
Table B.l. Amino acids in plasma Amino acid Taurine Aspartic acid Threonine Serine Asparagine Glutamic acid Glutamine Proline Glycine Alanine Citrulline a-Aminobutyrate Valine Cystine Methionine Isoleucine Leucine Tyrosine Phenylalanine Ornithine Lysine Histidine Tryptophan Arginine
Men
Women
(n;;;; 50) 3
(n:;; 15) 3
27-95 2- 9 92- 180 89- 165 32- 92 6- 62 466- 798 97-297 147- 299 146-494 19-47 15-35 179-335 24-54 13- 37 46- 90 113- 205 37- 77 46- 74 55- 135 135-243 72-108 25-65 28-96
18-66 3- 6 93- 197 78- 166 26- 74 6- 38 340- 696 112-220 100- 384 218-474 10-58 7-35 172- 248 31-49 14- 30 39- 67 98- 142 26-78 42- 62 36- 96 119-203 68-104 17-53 28- 108
Range = mean ± 2SD Modified from ref. [1]. b Modified from ref. [2]. C Modified from ref. [5]. d Modi
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