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Test Code C4U C4 Acylcarnitine, Quantitative, Urine

Reporting Name

C4 Acylcarnitine, QN, U

Useful For

Evaluation of patients with abnormal newborn screens showing elevations of iso-/butyrylcarnitine (C4) to aid in the differential diagnosis of short-chain acyl-CoA dehydrogenase and isobutyryl-CoA dehydrogenase deficiencies

Testing Algorithm

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

Method Name

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

Performing Laboratory

Mayo Medical Laboratories in Rochester

Specimen Type

Urine


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 (T068)

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
Urine Frozen (preferred) 7 days
  Refrigerated  24 hours

Reject Due To

Hemolysis

NA

Lipemia

NA

Icterus

NA

Other

NA

Reference Values

<3.00 millimoles/mole creatinine

Day(s) and Time(s) Performed

Monday, Wednesday, Friday; 8:00 a.m.

CPT Code Information

82017

LOINC Code Information

Test ID Test Order Name Order LOINC Value
C4U C4 Acylcarnitine, QN, U In Process

 

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

Analytic Time

2 days (not reported on Sunday)

Interpretation

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.

 

See Newborn Screening Follow-up for Isolated C4 Acylcarnitine Elevations (also applies to any plasma C4 acylcarnitine elevation) in Special Instructions for additional information.

Cautions

The results of urine acylcarnitines are typically not informative when the patient is receiving L-carnitine supplements.

Method Description

Acylcarnitines, including iso-butyrylcarnitine, are determined in urine by flow injection analysis tandem mass spectrometry using acetyl-d(3)-carnitine, propionyl-d(3)-carnitine, butyryl-d(3)-carnitine, octanoyl-d(3)-carnitine, dodecanoyl-d(3)-carnitine, and palmitoyl-d(3)-carnitine as internal standards. A total of 20 mcL of the diluted urine is extracted with an acidified acetonitrile solution containing the internal standards. The supernatant is evaporated and the residue treated with n-butanolic HCl yielding the acylcarnitines for analysis as their n-butyl esters.(Tortorelli S, Hahn SH, Cowan TM, et al: The urinary excretion of glutarylcarnitine is an informative tool in the biochemical diagnosis of glutaric acidemia type I. Mol Genet Metab 2005;84:137-143)

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, including the evaluation of C4 excretion in urine, is necessary to differentiate the 2 clinical entities. 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.

 

The American College of Medical Genetics (ACMG) newborn screening work group published diagnostic algorithms for the follow-up of infants who had a positive newborn screening result. For more information, see http://www.acmg.net.

 

See Newborn Screening Follow-up for Isolated C4 Acylcarnitine Elevations (also applies to any plasma C4 acylcarnitine elevation) in Special Instructions for additional information.

Specimen Retention Time

2 months

Genetics Test Information

Useful for differentiating the potential diagnoses of short chain acyl-CoA dehydrogenase (SCAD) versus isobutyryl-CoA dehydrogenase deficiency. The results are not informative when patient is receiving L-carnitine supplements.

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.

Forms

New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (T576) is available in Special Instructions.