CPT CODE:

USEFUL FOR:

Diagnosis of fatty acid beta-oxidation disorders and several organic acidurias
In general, more than 20 inborn errors of metabolism can be identifiedusing this method.  For most of the disorders involving fatty acid beta-oxidation, this is the most informative screening test. Quantitative acylcarnitine analysis can also be used to evaluate the treatment during follow-up of patients with these disorders.

SPECIMEN REQUIRED:

Draw blood in a green-top (sodium heparin) tube(s) just prior to ascheduled meal or feeding. Spin down and send 0.1 mL of sodium heparin plasma frozen in plastic vial.Note:    1. Include family history, clinical condition (asymptomatic                       or acute episode), diet, and drug therapy information.                  2. Patient's age is required on request form for                      processing.

TRANSPORT TEMPERATURE:

Frozen\Refrig NO\Ambient NO

CLINICAL INFORMATION:

Most disorders of fatty acid beta-oxidation and several organic acidurias can be diagnosed by acylcarnitine analysis, as each enzyme deficiency causes the accumulation of specific acyl-CoAs.  The acyl groups are being conjugated with carnitine and are easily measurable as acylcarnitines by tandem mass spectrometry (MS/MS). Based on newborn screening results using acylcarnitine analysis by MS/MS, the combined incidence of fatty acid beta-oxidation disorders and organic acidurias is approximately 1:8,000 live births. The clinical symptoms of fatty acid beta-oxidation disorders are similar, including hypoketotic hypoglycemia, a Reye-like syndrome, myopathy (involving skeletal and/or heart muscle), and sudden death. Organic acidurias also often present as acute life-threatening events early in life with metabolic acidosis, increased anion gap, and neurologic distress.  Patients with any of these disorders are at risk of developing fatal metabolic decompensations following acquisition of even common viral infections. Once diagnosed, these disorders can be treated by avoidance of fasting, special diets, and cofactor/vitamin supplementation.
See "Newborn Screening Follow-up for Isolated C4 Acylcarnitine Elevations", "Newborn Screening Follow-up for Elevations of C8, C6, and C10 Acylcarnitine", and "Newborn Screening Follow-up for Isolated C5 Acylcarnitines Elevations" in Special Instructions for additional information.

CLINICAL INTERPRETATION:

The quantitative results of the acylcarnitines support the interpretationof the complete profile but are not diagnostic by themselves.  
The interpretation is based on pattern recognition.  
Abnormal results are not sufficient to conclusively establish a diagnosis of a particular disease. To verify a preliminary diagnosis based on an acylcarnitine analysis, independent biochemical (e.g., in vitro enzyme assay) or molecular genetic analyses are required.
See "Newborn Screening Follow-up for Isolated C4 Acylcarnitine Elevations", "Newborn Screening Follow-up for Elevations of C8, C6, and C10 Acylcarnitine", and "Newborn Screening Follow-up for Isolated C5 Acylcarnitines Elevations" in Special Instructions for additional information.

REFERENCE VALUES:

Acetylcarnitine, C:2

1-7 days                2.14-15.89 nmol/mL

8 days-7 years    2.00-27.57 nmol/mL

> or = 8 years      2.00-17.83 nmol/mL

 

Propionylcarnitine, C3

1-7 days                <0.55 nmol/mL

8 days-7 years    <1.78 nmol/mL

> or = 8 years      <0.88 nmol/mL

 

Iso-/Butyrylcarnitine, C4

1-7 days                <0.46 nmol/mL

8 days-7 years    <1.06 nmol/mL

> or = 8 years      <0.83 nmol/mL

 

Isovaleryl-/2-Methylbutyrylcarnitine, C5

1-7 days                <0.38 nmol/mL

8 days-7 years    <0.63 nmol/mL

> or = 8 years      <0.51 nmol/mL

 

Hexanoylcarnitine, C6

1-7 days                <0.14 nmol/mL

8 days-7 years    <0.23 nmol/mL

> or = 8 years      <0.17 nmol/mL

 

3-OH-Hexanoylcarnitine, C6-OH

1-7 days                <0.08 nmol/mL

8 days-7 years    <0.19 nmol/mL

> or = 8 years      <0.09 nmol/mL

 

Octenoylcarnitine, C8:1

1-7 days                <0.48 nmol/mL

8 days-7 years    <0.91 nmol/mL

> or = 8 years      <0.88 nmol/mL

 

Octanoylcarnitine, C8

1-7 days                <0.19 nmol/mL

8 days-7 years    <0.45 nmol/mL

> or = 8 years      <0.78 nmol/mL

 

Decenoylcarnitine, C10:1

1-7 days