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Amino Acid Analysis

Amino Acid Analysis

Test Summary

Amino Acid Analysis

  

Clinical Use

  • Diagnose primary aminoacidopathies

  • Screen for secondary aminoacidopathies

  • Monitor therapeutic response

  • Assess nutritional status

Clinical Background

Primary aminoacidopathies are typically autosomal recessive or X-linked inherited disorders resulting from a deficient enzyme or transport protein. Over 30 aminoacidopathies have been described in the literature. Symptoms range from relatively benign to severe and may include, but are not limited to, growth and mental retardation, developmental delay, learning disabilities, seizures, lethargy, coma, vomiting, metabolic acidosis or alkalosis, sudden infant death syndrome (SIDS), osteomalacia, and osteoporosis. Depending on the natural history of the disorder, symptoms may be minimized or prevented by early diagnosis and treatment. Treatment may be based on dietary restrictions and/or supplementation with cofactors (eg, riboflavin or cobalamin) or conjugating agents (eg, carnitine or sodium benzoate).

Individuals Suitable for Testing

  • Neonates/infants

  • Children

  • Adults

Method

  • Liquid chromatography, mass spectrometry (LC/MS)

  • Analytical sensitivity: 0.02-4.5 �mol/L, depending on analyte

  • Analytical specificity: no known cross-reaction with other substances

  • Reportable range: 1.0-25,000 µmol/L

Reference Range

text

Reference ranges are provided in Tables 1-3 for plasma, urine, and CSF, respectively.

Table 1. Plasma Amino Acid Age-Specific Reference Ranges (µmol/L)

Amino Acid

<1 month

1-23 months

2-17 years

Adults (≥18 years)

Aspartic acid

2-20

2-14

1-8

1-4

Glutamic acid

51-277

32-185

9-109

10-97

Hydroxyproline

13-72

7-63

6-32

4-27

Serine

87-241

83-212

85-185

65-138

Asparagine

12-70

20-77

23-70

31-64

α-Aminoadipic acid

≤3

≤4

≤2

≤2

Glycine

133-409

103-386

138-349

122-322

Glutamine

240-1194

303-1459

405-923

428-747

Sarcosine

≤5

≤4

≤4

≤4

β-Alanine

≤8

≤8

≤5

≤5

Taurine

29-161

26-130

32-114

31-102

Histidine

40-143

42-125

54-113

60-109

Citrulline

3-35

4-50

9-52

16-51

Arginine

14-135

30-147

38-122

43-407

Threonine

56-392

40-428

59-195

67-198

Alanine

83-447

119-523

157-481

200-483

1-Methylhistidine

≤4

≤9

≤27

≤47

γ-Aminobutyric acid

<1

<1

≤2

≤3

3-Methylhistidine

≤10

≤8

1-6

2-9

β-Aminoisobutyric acid

≤9

≤8

≤6

<1

Proline

87-375

104-348

99-351

104-383

Ethanolamine

8-106

5-19

5-15

5-13

α-Aminobutyric acid

1-20

4-30

6-30

7-32

Tyrosinea

33-160

24-125

31-108

38-96

Valinea,b

57-250

84-354

130-307

132-313

Methionine

13-45

12-50

14-37

16-34

Cystathionine

<1

<1

<1

<1

Isoleucinea,b

12-92

10-109

33-97

34-98

Leucinea,b

23-172

43-181

65-179

73-182

Homocystine

<1

<1

<1

<1

Phenylalaninea

30-79

31-92

38-86

40-74

Tryptophana

17-85

16-92

30-94

40-91

Ornithine

29-168

19-139

33-103

27-83

Lysine

66-226

70-258

98-231

119-233

Alloisoleucineb

<1

<1

<1

<1

The full panel (test code 767X) includes all amino acids listed except alloisoleucine.

a Included in the limited panel (test code 1776X).

b Included in the MSUD panel (test code 19779X).

Table 2. Urine Amino Acid Age-Specific Reference Ranges (mmol/mol creatinine)

Amino Acid

<1 month

1-23 months

2-17 years

Adults (≥18 years)

Aspartic acid

≤7.0 ≤11.0 ≤2.0 ≤2.0

Glutamic acid

 4-19 3-30 ≤10.0 ≤3.0

Hydroxyproline

 30-485 2-345 ≤4.0 ≤2.0

Serine

 44-454 39-422 13-127 10-71

Asparagine

 8-42 5-132 3-42 2-37

α-Aminoadipic acid

 ≤10 ≤36 ≤34 ≤11

Glycine

 215-2053 105-413 23-413 ≤330

Glutamine

 ≤355 41-396 18-188 21-182

Sarcosine

 ≤18 ≤19 ≤2 ≤69

β-Alanine

 ≤9 ≤15 ≤5 ≤10

Taurine

 ≤650 ≤670 ≤255 ≤232

Histidine

 40-301 56-543 9-425 17-266

Citrulline

 ≤4 ≤13 ≤4 ≤2

Arginine

 ≤30 ≤35 ≤8 ≤5

Threonine

 ≤112 9-158 4-60 4-46

Alanine

 45-264 16-294 8-156 9-67
1-Methylhistidine ≤16 4-71 5-400 ≤204

γ-Aminobutyric acid

 ≤1 ≤2 ≤2 ≤2
3-Methylhistidine 9-45 14-35 11-40 10-35

β-Aminoisobutyric acid

 ≤269 ≤309 ≤133 ≤88

Proline

 ≤219 ≤216 ≤11 ≤2
Ethanolamine 87-490 54-176 27-114 21-65

α-Aminobutyric acid

 ≤7 ≤7 ≤5 ≤2

Tyrosine

 4-59 10-69 3-48 3-19

Valine

 2-20 4-21 2-20 2-5

Methionine

 ≤7 ≤7 ≤5 ≤2

Cystathionine

 2-20 ≤29 ≤8 ≤9
Isoleucine ≤9 ≤12 ≤5 ≤3

Leucine

 ≤23 ≤24 ≤13 ≤6

Homocystine

 <1.0 ≤4.0 <1.0 <1.0

Phenylalanine

 3-24 6-39 2-22 2-9

Tryptophan

 2-21 5-46 2-27 2-14

Ornithine

 ≤39 ≤11 ≤5 ≤4

Lysine

 13-284 4-239 3-112 3-59

Cystine

 15-48 6-28 3-20 3-13

Hydroxylysine

5-117

2-72

≤8

≤8

Table 3. CSF Amino Acid Age-Specific Reference Ranges (µmol/L)

Amino Acid

<3 months

3-23 months

2-10 years

>10 years

Aspartic acid

≤3 <1.0 <1.0 ≤2
Glutamic acid 1-9 ≤5 ≤11 1-13
Hydroxyproline 1-4 ≤2 <1 ≤2
Serine 30-88 22-61 15-62 9-41
Asparagine ≤27 ≤13 ≤25 ≤24
α-Aminoadipic acid <1 <1 <1 <1
Glycine 3-26 ≤12 ≤13 ≤10
Glutamine 525-1583 386-742 377-1738 361-1175
Sarcosine <1 <1 <1 <1
β-Alanine <1 <1 <1 <1
Taurine 0-18 ≤8 1-8 1-8
Histidine 8-32 4-25 7-25 7-22
Citrulline 1-4 ≤3 1-2 ≤2
Arginine 2-27 7-32 9-31 10-32
Threonine 23-104 10-55 8-85 12-64
Alanine 13-50 8-48 5-62 1-107
γ-Aminobutyric acid <1 <1 ≤2 ≤3
β-Aminoisobutyric acid <2 <2 <2 <2
Proline ≤4 ≤2 ≤2 ≤6
α-Aminobutyric acid ≤6 ≤6 1-11 1-11
Tyrosine 9-41 5-20 5-32 5-18
Valine 11-31 8-19 2-37 7-42
Methionine 2-14 1-7 ≤9 1-8
Isoleucine 3-11 3-7 2-13 3-10
Leucine 7-22 7-12 8-27 9-32
Homocystine <1 <1 ≤3 ≤2
Phenylalanine 4-31 4-14 ≤25 6-31
Tryptophan ≤6 ≤8 1-5 ≤9
Ornithine ≤26 ≤5 ≤5 ≤14
Lysine 6-38 3-29 9-58 19-60

Interpretive Information

Elevation of 1 or more amino acids may be diagnostic of an aminoacidopathy. Elevated amino acid levels are also associated with noninherited diseases such as severe liver disease and renal tubular disorders (eg, Fanconi syndrome). Decreased levels of amino acids are associated with malnutrition as seen in the elderly or those with poor protein intake or gastrointestinal disease.

Additional laboratory testing is required to diagnose other inherited disorders (ie, lactic acidosis, organic aciduria, and some urea cycle defects). Results should be evaluated in the context of clinical findings and/or additional test results.

Infant formulas that are supplemented with amino acids (particularly methionine and homocitrulline) and parenteral nutrition may affect the clinical accuracy of this test. Bacterial contamination of specimens and certain medications, such as valproic acid, can also affect the levels of specific amino acids. In addition, the absence of a protein-containing diet in newborns may preclude detection of selected aminoacidopathies.

Table 4 lists the amino acids that are elevated in the more common disorders.

Table 4. Common Aminoacidopathies and Associated Amino Acid Elevations

Common Aminoacidopathies

Elevated Amino Acids
Primary Aminoacidopathies

Arginase deficiency

 Arginine, glutamine

Arginosuccinase deficiency

 Argininosuccinate, glutamine

Citrullinemia

 Citrulline, glutamine

Cystinuria

 Cystine, ornithine, lysine, arginine (urine only)

Homocystinuria

 Homocystine

Maple syrup urine disease (MSUD)

 Valine, isoleucine, leucine, alloisoleucine

Phenylketonuria (PKU)

Phenylalanine

Tyrosinemia

Tyrosine
Secondary Aminoacidopathies     

Hyperammonemia

 Glutamine

Lactic acidosis

 Alanine

Organic acidurias, selected

 Glycine

Transient tyrosinemia of the newborn

 Tyrosine

References

  1. Part 8. Amino Acids. In: Scriver CR, Beaudet AL, Valle D, Sly WS, Childs B, Kinzler KW, Vogelstein B, eds. The Metabolic and Molecular Bases of Inherited Disease. 8th ed. New York, NY: McGraw-Hill, Inc; 2001;1665-2105.

  2. Part IV. Disorders of amino acid metabolism and transport. Fernandes J, Saudubray J-M, Van den Berghe G, eds. Inborn Metabolic Diseases Diagnosis and Treatment. 3rd ed. New York, NY: Springer; 2000;169-273.

  3. Part 2. Disorders of amino acid metabolism. Nyhan WL, Barshop BA, Ozand PT, eds. Atlas of Metabolic Diseases. 2nd ed. New York, NY: Oxford University Press Inc; 2005;109-189.

  4. Blau N, Duran M, Blaskovics ME, Gibson KM, eds. Physician’s Guide to the Laboratory Diagnosis of Metabolic Diseases. 2nd ed. New York, NY: Springer; 2003.
     

Content reviewed 12/2011
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