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Test ID: HCYSS Homocysteine, Total, Serum

Useful For

An aid for screening patients suspected of having an inherited disorder of methionine metabolism including:

-Cystathionine beta-synthase deficiency (homocystinuria)

-Methylenetetrahydrofolate reductase deficiency (MTHFR) and its thermolabile variants:

-Methionine synthase deficiency

-Cobalamin (Cbl) metabolism

-Combined methyl-Cbl and adenosyl-Cbl deficiencies: Cbl C2, Cbl D2, and Cbl F3 deficiencies

-Methyl-Cbl specific deficiencies: Cbl D-Var1, Cbl E, and Cbl G deficiencies

-Transcobalamin II deficiency

-Adenosylhomocysteinase (AHCY) deficiency

-Glycine N-methyltransferase (GNMT) deficiency

-Methionine adenosyltransferase (MAT) I/III deficiency

 

Screening and monitoring patients suspected of or confirmed with an inherited disorder of methionine metabolism

 

Evaluating individuals with suspected deficiency of B12 or folate

Reporting Name

Homocysteine, Total, S

Specimen Type

Serum


Specimen Required


Container/Tube:

Preferred: Red top

Acceptable: Serum gel tube

Specimen Volume: 1 mL

Collection Instructions: Centrifuge and aliquot serum into plastic vial within 4 hours of collection.


Specimen Minimum Volume

0.10 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Refrigerated (preferred) 28 days
  Frozen  309 days
  Ambient  28 days

Clinical Information

Homocysteine is an intermediary in the sulfur-amino acid metabolism pathways, linking the methionine cycle to the folate cycle. Inborn errors of metabolism that lead to homocysteinemia or homocystinuria include cystathionine beta-synthase deficiency (homocystinuria) and various defects of methionine remethylation. Genetic defects in vitamin cofactors (vitamins B6, B12, and folate) and nutritional deficiency of vitamin B12 and folate also lead to abnormal homocysteine accumulation.

 

Homocysteine concentration is an indicator of acquired folate or cobalamin deficiency, and is a contributing factor in the pathogenesis of neural tube defects. Homocysteine was also thought to be an independent predictor of cardiovascular disease (atherosclerosis, heart disease, thromboembolism), as early observational studies prior to the year 2000 linked homocysteine to cardiovascular risk and morbidity and mortality. However, following FDA-mandated folic acid supplementation in 1998, homocysteine concentrations decreased by approximately 10% without a similar change in cardiovascular or ischemic events. Currently, the use of homocysteine for assessment of cardiovascular risk is uncertain and controversial. Based on several meta-analyses, at present, homocysteine may be regarded as a weak risk factor for coronary heart disease, and there is a lack of direct causal relationship between hyperhomocysteinemia and cardiovascular disease. It is most likely an indicator of poor lifestyle and diet.

 

This test should be used in conjunction with plasma amino acids, quantitative acylcarnitines, methylmalonic acid, and urine organic acids to aid in the biochemical screening for primary and secondary disorders of methionine metabolism.

Reference Values

Age

Total Homocysteine (nmol/mL)

Female

Male

0-11 months

3.1 - 8.3

3.2 - 9.7

12-23 months

3.2 - 8.3

3.3 - 9.6

24-35 months

3.2 - 8.2

3.3 - 9.6

3 years

3.2 - 8.2

3.3 - 9.6

4 years

3.3 - 8.2

3.4 - 9.5

5 years

3.4 - 8.1

3.5 - 9.4

6 years

3.5 - 8.1

3.6 - 9.4

7 years

3.5 - 8.1

3.7 - 9.4

8 years

3.6 - 8.2

3.8 - 9.3

9 years

3.7 - 8.2

3.9 - 9.4

10 years

3.8 - 8.3

4.1 - 9.4

11 years

3.9 - 8.4

4.3 - 9.4

12 years

3.9 - 8.6

4.4 - 9.5

13 years

4.0 - 8.7

4.6 - 9.6

14 years

4.1 - 8.8

4.8 - 9.7

15 years

4.2 - 8.9

5.0 - 9.8

16 years

4.2 - 9.1

5.2 - 9.9

17 years

4.3 - 9.2

5.4 - 10.0

18 years

4.3 - 9.3

5.6 - 10.1

19 years

4.4 - 9.5

5.7 - 10.3

20 years

4.4 - 9.6

5.9 - 10.5

21 years

4.4 - 9.8

6.0 - 10.6

22 years

4.4 - 9.9

6.1 - 10.8

23 years

4.4 - 10.1

6.2 - 11.0

24 years

4.4 - 10.3

6.2 - 11.1

25 years

4.4 - 10.4

6.3 - 11.3

26 years

4.4 - 10.6

6.3 - 11.4

27 years

4.3 - 10.8

6.4 - 11.6

28 years

4.3 - 11.0

6.4 - 11.7

29 years

4.3 - 11.2

6.4 - 11.8

30 years

4.3 - 11.4

6.4 - 11.9

31 years

4.4 - 11.6

6.4 - 12.1

32 years

4.4 - 11.8

6.4 - 12.2

33 years

4.4 - 11.9

6.4 - 12.3

34 years

4.5 - 12.1

6.4 - 12.4

35 years

4.5 - 12.2

6.4 - 12.6

36 years

4.6 - 12.4

6.4 - 12.8

37 years

4.6 - 12.5

6.4 - 12.9

38 years

4.7 - 12.7

6.4 - 13.1

39 years

4.7 - 12.8

6.4 - 13.2

40 years

4.8 - 13.0

6.5 - 13.4

41 years

4.8 - 13.2

6.5 - 13.5

42 years

4.8 - 13.4

6.5 - 13.7

43 years

4.9 - 13.5

6.6 - 13.9

44 years

4.9 - 13.7

6.6 - 14.0

45 years

4.9 - 13.9

6.6 - 14.2

46 years

4.9 - 14.0

6.7 - 14.4

47 years

4.9 - 14.2

6.7 - 14.5

48 years

5.0 - 14.3

6.8 - 14.7

49 years

5.0 - 14.4

6.8 - 14.9

50 years

5.0 - 14.5

6.8 - 15.0

51 years

5.1 - 14.6

6.8 - 15.2

52 years

5.1 - 14.7

6.9 - 15.4

53 years

5.1 - 14.8

6.9 - 15.5

54 years

5.2 - 14.9

6.9 - 15.6

55 years

5.2 - 15.0

6.9 - 15.7

56 years

5.3 - 15.0

6.9 - 15.8

57 years

5.3 - 15.1

6.9 - 15.9

58 years

5.3 - 15.2

6.9 - 16.0

59 years

5.4 - 15.2

6.9 - 16.0

60 years

5.4 - 15.3

6.9 - 16.1

61 years

5.4 - 15.4

7.0 - 16.2

62 years

5.5 - 15.4

7.0 - 16.2

63 years

5.5 - 15.5

7.0 - 16.3

64 years

5.6 - 15.5

7.1 - 16.3

65 years

5.6 - 15.6

7.1 - 16.3

66 years

5.7 - 15.6

7.1 - 16.3

67 years

5.7 - 15.7

7.2 - 16.3

68 years

5.8 - 15.7

7.2 - 16.3

69 years

5.9 - 15.7

7.2 - 16.3

70 years

6.0 - 15.8

7.3 - 16.3

71 years

6.1 - 15.8

7.3 - 16.3

72 years

6.2 - 15.8

7.3 - 16.3

73 years

6.3 - 15.9

7.3 - 16.3

74 years

6.4 - 15.9

7.3 - 16.3

75 years

6.5 - 15.9

7.3 - 16.3

76 years

6.6 - 15.9

7.3 - 16.3

77 years

6.7 - 16.0

7.4 - 16.3

78 years

6.8 - 16.0

7.4 - 16.3

79 years

6.9 - 16.0

7.5 - 16.3

80 years

7.0 - 16.0

7.5 - 16.3

81 years

7.1 - 16.0

7.7 - 16.2

82 years

7.2 - 16.0

7.8 - 16.2

83 years

7.2 - 16.0

7.9 - 16.2

84 years

7.3 - 16.0

8.0 - 16.2

85 years

7.3 - 16.0

8.2 - 16.2

>85 years

7.4 - 16.0

8.3 - 16.2

Interpretation

Elevated homocysteine concentrations are considered informative in patients evaluated for suspected nutritional deficiencies (vitamin B12, folate) and inborn errors of metabolism. Measurement of methylmalonic acid (MMA) distinguishes between vitamin B12 (cobalamin) and folate deficiencies, as MMA is only elevated in vitamin B12 deficiency. Treatment response can be evaluated by monitoring serum homocysteine concentrations over time.

Clinical Reference

1. Harvey Mudd S, Levy HL, Kraus JP: Disorders of transsulfuration. In: Valle D, Beaudet AL, Vogelstein B eds. The Online Metabolic and Molecular Bases of Inherited Disease. McGraw-Hill, 2014. Accessed Oct 16, 2019. Available at ommbid.mhmedical.com/content.aspx?bookid=971&sectionid=62675596

2. Chrysant SG, Chrysant GS: The current status of homocysteine as a risk factor for cardiovascular disease: a mini review. Expert Review of Cardiovascular Therapy, 2018;16(8):559–565. doi: 10.1080/14779072.2018.1497974

3. Refsum H, Smith AD, Ueland PM, et al: Facts and recommendations about total homocysteine determinations: an expert opinion. Clin Chem. 2004 Jan;50:3-32

4. Turgeon CT, Magera MJ, Cuthbert CD, et al: Determination of total homocysteine, methylmalonic acid, and 2-methylcitric acid in dried blood spots by tandem mass spectrometry. Clin Chem. 2010 Nov;56:1686-1695

5. Sacharow SJ, Picker JD, Levy HL: Homocystinuria caused by cystathionine beta-synthase deficiency. In: Adam MP, Ardinger HH, Pagon RA, et al, eds. GeneReviews [Internet] University of Washington, Seattle. 2004. Updated May 18, 2017. Accessed September 11, 2020. Available at www.ncbi.nlm.nih.gov/books/NBK1524/

Day(s) and Time(s) Performed

Monday through Friday; 8 a.m.

Analytic Time

3 days (not reported on Saturday or Sunday)

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the U.S. Food and Drug Administration.

CPT Code Information

83090

LOINC Code Information

Test ID Test Order Name Order LOINC Value
HCYSS Homocysteine, Total, S 13965-9

 

Result ID Test Result Name Result LOINC Value
35836 Homocysteine, Total, S 13965-9

Method Name

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Forms

1. Biochemical Genetics Patient Information (T602) in Special Instructions.

2. If not ordering electronically, complete, print, and send an Inborn Errors of Metabolism Test Request (T798) with the specimen.

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