C5-OH acylcarnitine (3-hydroxyisovaleryl/3-hydroxy-2-methylbutyryl)

This test measures C5-OH acylcarnitines in blood, specifically 3-hydroxyisovalerylcarnitine and 3-hydroxy-2-methylbutyrylcarnitine. These molecules are formed when your body breaks down the amino acids leucine and isoleucine and are carried in the blood attached to carnitine.

Results help assess how well certain enzymes in these pathways are working. The test is commonly included in an acylcarnitine profile used in newborn screening and in evaluations for suspected inborn errors of metabolism.

C5-OH acylcarnitines can rise when there are problems with enzymes involved in leucine or isoleucine metabolism, such as 3-methylcrotonyl-CoA carboxylase deficiency, multiple carboxylase deficiency related to biotin pathways, or related metabolic conditions. Identifying these issues early can guide nutrition and medical management to prevent complications.

Your clinician may order this test to follow up an abnormal newborn screen, investigate unexplained episodes of poor feeding, vomiting, lethargy, or metabolic acidosis, or to monitor a known metabolic disorder. It can also help distinguish transient findings from conditions that need ongoing care.

A single mildly abnormal result can happen for temporary reasons, such as illness, fasting, or recent changes in diet or supplements. Your clinician will look at the pattern of acylcarnitines, your symptoms, and other labs to decide whether the finding is meaningful.

If the value is persistently elevated or clearly abnormal, follow-up testing may include urine organic acids, plasma amino acids, and sometimes enzyme or genetic testing. Management often focuses on avoiding catabolic stress, adjusting protein intake, and using targeted vitamins or carnitine when appropriate. Discuss any concerns with your care team, who will put the result in context and create a plan that fits your situation.