Test ID: ACRN
Acylcarnitines, Quantitative, Plasma
Useful For 
Suggests clinical disorders or settings where the test may be helpful
Diagnosis of fatty acid beta-oxidation disorders and several organic acidurias
Evaluate the treatment during follow-up of patients with these disorders
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
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 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 in 2,000 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 due to minor stressors such as fasting or 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.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Acetylcarnitine, C2
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: <0.25 nmol/mL
8 days-7 years: <0.46 nmol/mL
> or =8 years: <0.47 nmol/mL
Decanoylcarnitine, C10
1-7 days: <0.27 nmol/mL
8 days-7 years: <0.91 nmol/mL
> or =8 years: <0.88 nmol/mL
Glutarylcarnitine, C5-DC
1-7 days: <0.06 nmol/mL
8 days-7 years: <0.10 nmol/mL
> or =8 years: 0.11 nmol/mL
Dodecenoylcarnitine, C12:1
1-7 days: <0.19 nmol/mL
8 days-7 years: <0.37 nmol/mL
> or =8 years: <0.35 nmol/mL
Dodecanoylcarnitine, C12
1-7 days: <0.18 nmol/mL
8 days-7 years: <0.35 nmol/mL
> or =8 years: <0.26 nmol/mL
3-OH-Dodecanoylcarnitine, C12-OH
1-7 days: <0.06 nmol/mL
8 days-7 years: <0.09 nmol/mL
> or =8 years: <0.08 nmol/mL
Tetradecadienoylcarnitine, C14:2
1-7 days: <0.09 nmol/mL
8 days-7 years: <0.13 nmol/mL
> or =8 years: <0.18 nmol/mL
Tetradecenoylcarnitine, C14:1
1-7 days: <0.16 nmol/mL
8 days-7 years: <0.35 nmol/mL
> or =8 years: <0.24 nmol/mL
Tetradecanoylcarnitine, C14
1-7 days: <0.11 nmol/mL
8 days-7 years: <0.15 nmol/mL
> or =8 years: <0.12 nmol/mL
3-OH-Tetradecenoylcarnitine, C14:1-OH
1-7 days: <0.06 nmol/mL
8 days-7 years: <0.18 nmol/mL
> or =8 years: <0.13 nmol/mL
3-OH-Tetradecanolycarnitine, C14-OH
1-7 days: <0.04 nmol/mL
8 days-7 years: <0.05 nmol/mL
> or =8 years: <0.08 nmol/mL
Hexadecenoylcarnitine, C16:1
1-7 days: <0.15 nmol/mL
8 days-7 years: <0.21 nmol/mL
> or =8 years: <0.10 nmol/mL
Hexadecanoylcarnitine, C16
1-7 days: <0.36 nmol/mL
8 days-7 years: <0.52 nmol/mL
> or =8 years: <0.23 nmol/mL
3-OH-Hexadecenoylcarnitine, C16:1-OH
1-7 days: <0.78 nmol/mL
8 days-7 years: <0.36 nmol/mL
> or =8 years: <0.06 nmol/mL
3-OH-Hexadecanoylcarnitine, C16-OH
1-7 days: <0.10 nmol/mL
8 days-7 years: <0.07 nmol/mL
> or =8 years: <0.06 nmol/mL
Linoleylcarnitine, C18:2
1-7 days: <0.12 nmol/mL
8 days-7 years: <0.31 nmol/mL
> or =8 years: <0.24 nmol/mL
Oleylcarnitine, C18:1
1-7 days: <0.25 nmol/mL
8 days-7 years: <0.45 nmol/mL
> or =8 years: <0.39 nmol/mL
Stearoylcarnitine, C18
1-7 days: <0.10 nmol/mL
8 days-7 years: <0.12 nmol/mL
> or =8 years: <0.14 nmol/mL
3-OH-Linoleylcarnitine, C18:2-OH
1-7 days: <0.04 nmol/mL
8 days-7 years: <0.06 nmol/mL
> or =8 years: <0.06 nmol/mL
3-OH-Oleylcarnitine, C18:1-OH
1-7 days: <0.03 nmol/mL
8 days-7 years: <0.04 nmol/mL
> or =8 years: <0.06 nmol/mL
Interpretation Provides information to assist in interpretation of the test results
An interpretive report is provided. The individual quantitative results support the interpretation of the acylcarnitine 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 (eg, in vitro enzyme assay) or molecular genetic analyses are required.
For information on the follow up of specific acylcarnitine elevations, see Special Instructions for the following algorithms: 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.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
In a few instances, false-negative results occur in the analysis of acylcarnitine profiles. For some disorders, such as medium-chain acyl-CoA dehydrogenase (MCAD) deficiency, the calculation of ratios between different acylcarnitine species provides a discriminate factor to overcome such problems. Where applicable, the calculation of such ratios will be incorporated in the routine acylcarnintine analysis. Informative profiles may also not be detected in some disorders where the accumulation of diagnostic acylcarnitines is a reflection of the residual activity of the defective enzyme, the dietary load of precursors, and the anabolic/catabolic and treatment status of a patient.
Patients with carnitine deficiency may not exhibit abnormally high acylcarnitine concentrations. If the results are indicative for carnitine deficiency, the interpretation will include a remark that this limits the diagnostic value of the test and repeat analysis may be considered following carnitine supplementation.
Follow up testing such as in vitro enzyme assays or molecular genetic testing may be recommended following abnormal acylcarnitine results. It is not advisable to intentionally stress the patient's metabolism (eg, fasting test) prior to specimen collection for acylcarnitine analysis.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
1. Matern D: Acylcarnitines, including in vitro loading tests. In: Blau N, Duran M, Gibson KM, eds. Laboratory Guide to the Methods in Biochemical Genetics, Springer Verlag 2008:171-206
2. Rinaldo P, Cowan TM, Matern D: Acylcarnitine profile analysis. Genet Med 2008;10:151-156
3. Smith EH, Matern D: Acylcarnitine analysis by tandem mass spectrometry. Curr Protoc Hum Genet. 2010;Chapter 17:Unit 17.8.1-20
Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test
- Newborn Screening Follow-up for Isolated C4 Acylcarnitine Elevations (also applies to any plasma C4 acylcarnitine elevations)
- Newborn Screening Follow-up for Elevations of C8, C6, and C10 Acylcarnitine (also applies to any plasma C8, C6, and C10 acylcarnitine elevations)
- Newborn Screening Follow-up for Isolated C5 Acylcarnitines Elevations (also applies to any plasma C5 acylcarnitine elevation)
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