C5 Isobars
Description:
The C5 isobar test is a second line screening test which is indicated when an increased C5 carnitine result is obtained by Newborn Screening Programme Centre. Four different isobars (isovalerylcarnitine, pivaloylcarnitine, valerylcarnitine and 2-methylbutyrylcarnitine) can contribute to C5 increase. The aim of the test is to identify which compound is present in the sample to aid interpretation of the screening result.
Reference range:
Qualitative analysis only - results are reported as an interpretive comment.
Department:
Location:
Sample type and Volume required:
Capillary blood spotted onto a Newborn Screening blood spot card (Guthrie card). Minimum one spot of 7 mm diameter.
Call in advance:
Yes
Turnaround time:
Same day from SE Thames NBS lab, five working days for samples from external NBS laboratories.
Special sample instructions:
Allow to dry at room temperature prior to packaging.
Storage and transport:
Send via first class post. Samples should be received within the laboratory within 14 days of collection.
Contacts:
For clinical advice or interpretation of results, please contact the laboratory in the first instance.
Last updated: 30/01/2026
