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Test ID: C4U C4 Acylcarnitine, Quantitative, Random, Urine

Reporting Name

C4 Acylcarnitine, QN, U

Useful For

Evaluation of patients with abnormal newborn screens showing elevations of iso-/butyrylcarnitine to aid in the differential diagnosis of short-chain acyl-CoA dehydrogenase and isobutyryl-CoA dehydrogenase deficiencies

Specimen Type


Ordering Guidance

This second-tier test is used specifically to evaluate a newborn screening elevation of iso-/butyrylcarnitine and must not be ordered with either C5OHU / C5-OH Acylcarnitine, Quantitative, Random, Urine or C5DCU / C5-DC Acylcarnitine, Quantitative, Random, Urine.


For general screening for metabolic disorders, see OAU / Organic Acids Screen, Random, Urine; ACRN / Acylcarnitines, Quantitative, Plasma; and AAQP / Amino Acids, Quantitative, Plasma.

Necessary Information

Include patient's age, family history, clinical condition (asymptomatic or acute episode), diet, and drug therapy information.

Specimen Required

Patient Preparation: If clinically feasible, discontinue L-carnitine supplementation at least 72 hours before specimen collection.

Supplies: Urine Tubes, 10 mL (T068)

Collection Container/Tube: Clean, plastic urine collection container

Submission Container/Tube: Plastic, 10 mL urine tube

Specimen Volume: 5 mL

Collection Instructions:

1. Collect a random urine specimen.

2. Freeze specimen immediately.

Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Urine Frozen (preferred) 7 days
  Refrigerated  24 hours

Reference Values

<3.00 millimoles/mole creatinine

Day(s) Performed

Monday, Wednesday, Friday

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 US Food and Drug Administration.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
C4U C4 Acylcarnitine, QN, U 53111-1


Result ID Test Result Name Result LOINC Value
88829 C4 Acylcarnitine, QN, U 53111-1
28075 C4 Interpretation 59462-2
34468 Reviewed By 18771-6

Clinical Information

An isolated elevation of iso-/butyrylcarnitine (C4) in plasma or newborn screening blood spots is related to a diagnosis of either short chain acyl-CoA dehydrogenase (SCAD) deficiency or isobutyryl-CoA dehydrogenase (IBD) deficiency. Diagnostic testing by acylcarnitine analysis, including the evaluation of C4 excretion in urine, is necessary to differentiate the 2 clinical entities.(1) Patients with IBD deficiency excrete an abnormal amount of C4 acylcarnitine in urine, whereas patients with SCAD deficiency can have a normal excretion of this metabolite.


See Newborn Screening Follow-up for Isolated C4 Acylcarnitine Elevations (also applies to any plasma or serum C4 acylcarnitine elevation) for additional Information.


Almost all patients with isobutyryl-CoA dehydrogenase deficiency excrete an abnormal amount of iso-/butyrylcarnitine (C4) in their urine. Some, but not all, affected individuals also excrete elevated levels of isobutyrylglycine. Conversely, patients with short-chain acyl-CoA dehydrogenase deficiency can have a normal excretion of C4.

Clinical Reference

Clinical Reference

1. Miller MJ, Cusmano-Ozog K, Oglesbee D, Young S; ACMG Laboratory Quality Assurance Committee: Laboratory analysis of acylcarnitines, 2020 update: a technical standard of the American College of Medical Genetics and Genomics (ACMG). Genet Med. 2021 Feb;23(2):249-258 

2. Oglesbee D, Vockley J, Ensenauer RE, et al: Ten cases of isobutyryl-CoA dehydrogenase (IBDH) deficiency detected by newborn screening. J Inherit Metab Dis. 2005;28(Suppl 1):13. doi: 10.1007/s10545-004-0001-x

3. Oglesbee D, He M, Majumder N, et al: Development of a newborn screening follow-up algorithm for the diagnosis of isobutyryl-CoA dehydrogenase deficiency. Genet Med. 2007 Feb;9(2):108-116

Report Available

2 to 5 days

Method Name

Flow Injection Analysis-Tandem Mass Spectrometry (FIA-MS/MS)

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