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Unit Code 88829:
C4 Acylcarnitine, Quantitative, Urine

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Useful For

Evaluation of patients with abnormal newborn screens showing

elevations of C4 to aid in the differential diagnosis of SCAD

deficiency and IBD deficiency

Clinical Information

An isolated elevation of iso-butyrylcarnitine (C4) in newborn screening

blood spots is related to a diagnosis of either short-chain acyl-CoA

dehydrogenase (SCAD) deficiency or isobutyryl-CoA dehydrogenase

(IBD) deficiency. Follow-up confirmatory and diagnostic testing is

necessary to differentiate the 2 clinical entities. 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-see

http://www.acmg.net/resources/policies/ACT/Visio-C4_(4-19-06).pdf.

Evaluation of C4 excretion in urine is part of the recommended diagnostic

workup, as it is useful for differentiating between SCAD deficiency and IBD

deficiency.

 

See "Newborn Screening Follow-up for Isolated C4 Acylcarnitine

Elevations" in Special Instructions for additional information.

Reference Values

<3.00 millimoles/mole creatinine

Interpretation

Almost all patients with IBD deficiency excrete an abnormal amount

of C4 in their urine. Some, but not all, affected individuals also

over excrete isobutyrylglycine. Conversely, patients with SCAD

deficiency can have a normal excretion of C4.

 

See "Newborn Screening Follow-up for Isolated C4 Acylcarnitine

Elevations" in Special Instructions for additional information.

Cautions

The results of urine acylcarnitines are not informative when

the patient is receiving L-carnitine supplements.

Special Instructions and Forms

• Newborn Screening Follow-up for Isolated C4 Acylcarnitine Elevations (also applies to any plasma C4 acylcarnitine elevations) 

Clinical Reference

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

Key