Most families find out through the newborn screening heel prick, which flags low carnitine in the baby's blood. A flag is not a final answer. A metabolic specialist confirms it with a few more tests, and some babies turn out to have low carnitine for a different reason. Either way, a healthy, feeding baby is not in immediate danger while you wait.
You probably got a phone call about your baby's newborn screen. The words were clinical. The timeline felt urgent. And if you are being honest, you may have spent the hours since then online in a way that did not help.
Take a deep breath. A positive newborn screen for Primary Carnitine Deficiency does not mean your baby is in danger right now. It does not mean you missed something. Newborn screening exists so that conditions like PCD are found before any symptoms appear, and that is most likely exactly what just happened. Your baby was screened. Something was flagged. Now you take the next steps, one at a time.
What did the newborn screen find?
The newborn screen found a low level of free carnitine (written as "C0" on the lab report) in a few drops of your baby's blood. That heel-prick sample is tested for dozens of conditions. When one comes back outside the expected range, it means "look closer," not "this is confirmed."
Two things can be true after a low-carnitine flag. One: your baby has PCD and will do well with lifelong treatment. Two: the carnitine is low for another reason. The most common other reason is that the mother's own carnitine is low (a maternal carnitine deficiency). A baby's early carnitine comes from mom, so a low level in the baby can actually point to the mother. That is common and simple to check. In that case your baby may not have PCD at all. Confirmation testing sorts this out, and nothing about this step is an emergency.
How is the diagnosis confirmed?
A metabolic specialist or genetics clinic confirms PCD with a few follow-up tests, usually within days of the screen. Those may include:
- A detailed blood test for carnitine levels (a plasma acylcarnitine profile), which also rules out some related conditions.
- A urine test (urine organic acids) that shows how the body is handling certain nutrients.
- A genetic test of the SLC22A5 gene, which finds the specific change that confirms PCD.
- A carnitine test for the mother, because low carnitine in mom can cause a low result in a baby who does not have PCD.
Waiting is hard when you want answers. Here is what I can tell you: a baby who looks well and is feeding normally is at very low risk during this short waiting period. If no one from a metabolic clinic has called you yet, call your pediatrician and ask for the referral. You should be seen promptly, and it is fine to say so.
What does a PCD diagnosis mean for the rest of the family?
A PCD diagnosis usually means both parents are carriers, and it is worth asking about testing for siblings. PCD is passed down when a child gets one changed copy of the gene from each parent (autosomal recessive). Carriers are healthy and usually do not know. A regular carnitine blood level is not a reliable way to find carriers; a genetic test of the SLC22A5 gene is. A genetic counselor can walk you through what this means for other children and for any future pregnancies, at whatever pace you want.
I'm a person living with PCD, not your doctor. Everything here is to help you understand and ask good questions; your child's metabolic team makes the medical decisions.
Last updated October 2026.
Where this comes from
I wrote this page from the studies below and from living with PCD. Your care team is the final word on your child.
- Magoulas PL, El-Hattab AW. "Systemic primary carnitine deficiency: an overview of clinical manifestations, diagnosis, and management." Orphanet Journal of Rare Diseases, 2012. https://doi.org/10.1186/1750-1172-7-68
- Longo N. "Primary Carnitine Deficiency and Newborn Screening for Disorders of the Carnitine Cycle." Annals of Nutrition & Metabolism, 2016. https://doi.org/10.1159/000448321
- Frigeni M, Balakrishnan B, Yin X, et al. "Functional and molecular studies in primary carnitine deficiency." Human Mutation, 2017. https://doi.org/10.1002/humu.23315