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Interpretive Handbook

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Test 88829 :
C4 Acylcarnitine, Quantitative, Urine

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

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 further 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.

Useful For Suggests clinical disorders or settings where the test may be helpful

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

Interpretation Provides information to assist in interpretation of the test results

Almost all patients with isobutyryl-CoA dehydrogenase deficiency excrete an abnormal amount of 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 Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

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

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.

<3.00 millimoles/mole creatinine

Clinical References Provides recommendations for further in-depth reading of a clinical nature

Oglesbee D, Vockley J, Ensenauer RE, et al: Ten cases of isobutyryl-CoA dehydrogenase (IBDH) deficiency detected by newborn screening. JIMD 2005;28(Suppl 1):13


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