Expanded Acylcarnitine Analysis (Test 4000)

CPT Code(s): 82017

Ordering Recommendation: This test is intended to be used in the diagnosis and clinical management of patients with inborn errors of metabolism related to fatty acid oxidation and organic acidemias. This test, or a targeted subpanel version of this test (TESTs 4010–4060), is also the preferred follow-up acylcarnitine assay when newborn screen results identify an ambiguous acylcarnitine elevation (see targeted subpanels below).

This advanced method was developed by our laboratory as an improved alternative to current acylcarnitine testing (Luna et al. (2022); PMID 34954532). This test quantifies 61 analytes including all acylcarnitine species in our basic acylcarnitine analysis (TEST 2000) with the advantage of providing unambiguous separation and quantification of clinically important isomeric/isobaric acylcarnitines. This method includes clinically relevant ratio calculations and quantifies an expanded list of analytes including free carnitine, carnitine metabolic precursors, and long chain dicarboxylic acylcarnitines useful in the diagnosis of peroxisomal disorders.

Targeted subpanels of TEST 4000 are available (TESTs 4010-4060). Specimens are subjected to the TEST 4000 workflow but only the targeted analytes are reported. These tests may be considered to follow-up on flow injection acylcarnitine results (such as “basic acylcarnitine analysis” TEST 2000 or Newborn Screening) that do not clarify acylcarnitine isomer identity or when there is a high clinical concern for a specific metabolic disorder targeted by these panels. If multiple panels are considered, it is more cost effective to order TEST 4000.

Targeted Acylcarnitine Subpanels

• TEST 4010: C3:DC / C4:OH Acylcarnitines
  • Reported analytes:
    • malonylcarnitine (C3:DC)
    • hydroxy(iso)butyrylcarnitine (C4:OH)
• TEST 4040: C4:DC / C5:OH Acylcarnitine Isomers
  • Reported analytes:
    • propionylcarnitine (C3)
    • tiglylcarnitine (C5:1)
    • 3-methylcrotonylcarnitine (C5:1)
    • 3-hydroxyisovalerylcarnitine (C5:OH)
    • methylmalonylcarnitine (C4:DC)
    • succinylcarnitine (C4:DC)
    • C3/C2 (Ratio)
• TEST 4020: C4 Acylcarnitine Isomers
  • Reported analytes:
    • isobutyrylcarnitine (C4)
    • butyrylcarnitine (C4)
• TEST 4030: C5 Acylcarnitine Isomers
  • Reported analytes:
    • pivaloylcarnitine (C5)
    • 2-methylbutyrylcarnitine (C5)
    • isovalerylcarnitine (C5)
    • valerylcarninitine (C5)
• TEST 4050: Long Chain Dicarboxylic Acylcarnitines
  • Reported analytes:
    • hexadecanedioylcarnitine (C16:DC)
    • octadecenedioylcarnitine (C18:1:DC)
    • octadecanedioylcarnitine (C18:DC)
    • eicosanedioylcarnitine (C20:DC)
    • docosanedioylcarnitine (C22:DC)
• TEST 4060: Carnitine Metabolism Panel
  • Reported analytes:
    • carnitine (C0)
    • deoxycarnitine (DXY)
    • trimethylamine-N-oxide (TMAO)
    • trimethyllysine (TML)
    • TML/DXY (RATIO) 

Synonyms: Acylcarnitine Analysis with Isobaric resolution by LC-MS/MS, Expanded acylcarnitine analysis by LC-MS/MS

Methodology: Liquid chromatography tandem mass spectrometry (LC-MS/MS)

Performed: Biweekly

Reported: 14 days or less

Patient Preparation: None required

Specimen Type: frozen plasma/serum

Collection Tube (preferred): sodium heparin (green top)

Collection Tube (other acceptable): lithium heparin (green top), serum (red top)

Processing: Separate plasma/serum from whole blood and transfer to a plastic transport tube and freeze as soon as possible. If multiple different tests are ordered, submitting separate frozen aliquots for each may improve TAT.

Specimen Volume: 0.5 mL (minimum of 0.1 mL)

Storage: Must be stored at -20°C

Shipment: Ship samples frozen on 3-5 lbs. of dry ice in an insulated container using overnight courier.

Unacceptable Conditions:

• Specimen requirements listed above not met.
• Sample fully thawed during shipment.
• Sample has excessive hemolysis or clotting.
• Sample collected in gel tube (plasma separator tube (PST) or serum separator tube (SST).

Stability: 90 days in the freezer (-20°C)

Reference Interval: by report 

Interpretation: A brief interpretation of results is provided with each test.

Limitations: If rapid results are needed, we recommend ordering our basic acylcarnitine analysis (TEST 2000).

False negative results can occur in rare situations when diet, treatment or secondary carnitine depletion causes acylcarnitine levels to appear normal in an affected individual. Values are most informative when compared to the provided laboratory specific normal range.

Results should be interpreted in the context of clinical symptoms and concurrent testing. In the case of a new diagnosis, acylcarnitine results should be confirmed with additional biochemical or molecular genetic testing.

This test was developed, and its performance characteristics determined, by Indiana University Biochemical Genetics Laboratory. It has not been cleared or approved by the U.S. Food and Drug Administration. This test is used for clinical purposes. It should not be regarded as investigational or for research. The laboratory is certified under the Clinical Laboratory Improvement Amendments of 1988 (CLIA ’88) as qualified to perform high complexity clinical laboratory testing. CLIA# 15D0647198, CAP# 1678930

References:

1. Luna, C., Griffin, C, and Miller, M. J. (2022). "A clinically validated method to separate and quantify underivatized acylcarnitines and carnitine metabolic intermediates using mixed-mode chromatography with tandem mass spectrometry" J Chromatogr A. 1663: 462749
2. Miller MJ, Cusmano-Ozog K, Oglesbee D, Young S (2020). "Laboratory analysis of acylcarnitines, 2020 update: a technical standard of the American College of Medical Genetics and Genomics (ACMG)." Genet Med 2021;23:249-58.