Medical Conditions

MCADD (Medium-Chain Acyl-CoA Dehydrogenase Deficiency) in Babies

Medically reviewed by Dr. Michael Okonkwo, MD, FAAP · Board-Certified Neonatologist

Content reviewed against published NIH, HRSA, ACMG guidelines

Editorial policy

Last reviewed:

If your baby has been diagnosed with or you suspect mcadd (medium-chain acyl-coa dehydrogenase deficiency) in babies, here is what the evidence says.

The short answer

MCADD (medium-chain acyl-CoA dehydrogenase deficiency) is the most common fatty acid oxidation disorder, affecting approximately 1 in 15,000 to 20,000 births. Babies with MCADD cannot properly break down medium-chain fats for energy during periods of fasting or illness. This can lead to dangerously low blood sugar (hypoglycemia), lethargy, seizures, and liver failure. MCADD is detected through newborn screening, and with proper management — primarily avoiding prolonged fasting — children with MCADD can live completely healthy lives.

Key takeaways

  • MCADD (medium-chain acyl-CoA dehydrogenase deficiency) is the most common fatty acid oxidation disorder, affecting approximately 1 in 15,000 to 20,000 births. Babies with MCADD cannot properly break down medium-chain fats for energy during periods of fasting or illness. This can lead to dangerously low blood sugar (hypoglycemia), lethargy, seizures, and liver failure. MCADD is detected through newborn screening, and with proper management — primarily avoiding prolonged fasting — children with MCADD can live completely healthy lives.
  • Usually normal when: Your baby's newborn screening came back normal for MCADD
  • Call your doctor if: Your baby with MCADD is ill and has not been able to eat for more than 4 hours (infants) or 6-8 hours (older babies) — go to the emergency room for IV glucose with your metabolic emergency letter
  • Varies by age — see the age-by-age breakdown below
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What Parents Should Know

According to NIH, HRSA, ACMG guidelines, mCADD (medium-chain acyl-CoA dehydrogenase deficiency) is the most common fatty acid oxidation disorder, affecting approximately 1 in 15,000 to 20,000 births. Babies with MCADD cannot properly break down medium-chain fats for energy during periods of fasting or illness. This can lead to dangerously low blood sugar (hypoglycemia), lethargy, seizures, and liver failure. MCADD is detected through newborn screening, and with proper management — primarily avoiding prolonged fasting — children with MCADD can live completely healthy lives. At 0-1 week, newborns with MCADD are at immediate risk because they have limited energy stores and must eat frequently. Before newborn screening results are available, undiagnosed babies can develop a metabolic crisis if they go too long without feeding. This is why it is important for all newborns to feed every 2-3 hours in the first days of life. If newborn screening detects MCADD, your baby's medical team will counsel you on safe fasting intervals and create an emergency plan. It is generally considered normal when your baby's newborn screening came back normal for MCADD. However, you should contact your pediatrician promptly if your baby with MCADD is ill and has not been able to eat for more than 4 hours (infants) or 6-8 hours (older babies) — go to the emergency room for IV glucose with your metabolic emergency letter.

Sources: [1], [2], [3]

Normal vs. Concerning

Usually Normal
Worth Discussing
Your baby's newborn screening came back normal for MCADD
Your baby with MCADD is ill and has not been able to eat for more than 4 hours (infants) or 6-8 hours (older babies) — go to the emergency room for IV glucose with your metabolic emergency letter
Your baby with MCADD is feeding well, growing normally, and has had no metabolic crises
Your baby with MCADD becomes lethargic, unusually sleepy, difficult to wake, or has seizures — call 911 and tell them your child has a metabolic disorder
An initial positive screen was followed by confirmatory testing that showed the baby does not have MCADD — some variants detected on screening are benign
Your baby with MCADD is vomiting and cannot keep any food or fluids down — do not wait for the next scheduled feeding, seek emergency care immediately
Your child with MCADD is eating regularly, following the fasting guidelines, and has an emergency plan in place
An undiagnosed newborn becomes extremely lethargic, is difficult to wake for feedings, or has seizures in the first days of life before newborn screening results return

When to Seek Immediate Care

  • Your baby with MCADD is ill and has not been able to eat for more than 4 hours (infants) or 6-8 hours (older babies) — go to the emergency room for IV glucose with your metabolic emergency letter
  • Your baby with MCADD becomes lethargic, unusually sleepy, difficult to wake, or has seizures — call 911 and tell them your child has a metabolic disorder
  • Your baby with MCADD is vomiting and cannot keep any food or fluids down — do not wait for the next scheduled feeding, seek emergency care immediately
  • An undiagnosed newborn becomes extremely lethargic, is difficult to wake for feedings, or has seizures in the first days of life before newborn screening results return

By Age

What to expect by age

0-1 week

Newborns with MCADD are at immediate risk because they have limited energy stores and must eat frequently. Before newborn screening results are available, undiagnosed babies can develop a metabolic crisis if they go too long without feeding. This is why it is important for all newborns to feed every 2-3 hours in the first days of life. If newborn screening detects MCADD, your baby's medical team will counsel you on safe fasting intervals and create an emergency plan.

1-6 months

Babies diagnosed with MCADD through newborn screening should not go more than 4 hours without feeding. Breastfeeding and formula feeding are both safe. No special formula or dietary changes are needed — the key is preventing prolonged fasting. During illness, even minor ones like colds with decreased appetite, extra vigilance is required to ensure adequate calorie intake. Your metabolic team will provide a sick-day emergency letter to carry at all times and may recommend a cornstarch-based supplement for emergency use.

6-12 months

As your baby begins eating solid foods, the risk of metabolic crisis during normal daily life decreases because meals and snacks are more frequent and energy reserves improve. However, illness remains the most dangerous time — vomiting, diarrhea, or fever that reduces food intake can trigger a crisis within hours. Safe fasting intervals gradually increase as your baby grows (up to about 8 hours by age 1), but your metabolic team will provide specific guidance. Always have your emergency plan ready.

1-3 years

Toddlers with MCADD can eat a normal diet with no protein or fat restriction. The main management principle continues to be avoiding prolonged fasting — safe intervals extend to about 10-12 hours by age 2-3, but during illness, fasting tolerance drops significantly. Many families find it helpful to give a bedtime snack with complex carbohydrates. If your toddler is vomiting and cannot keep food down for more than a few hours, go to the emergency room for IV glucose — do not wait to see if things improve.

Older children and adults

With ongoing awareness of fasting limits and proper sick-day management, children and adults with MCADD lead normal, healthy lives. Most learn to self-manage by recognizing early signs of low blood sugar (irritability, shakiness, pallor) and eating promptly. Exercise management may be discussed, as prolonged intense exercise can also deplete energy stores. MCADD is a lifelong condition but does not limit life expectancy when properly managed.

What to Tell Your Pediatrician

  • Describe when you first noticed mcadd (medium-chain acyl-coa dehydrogenase deficiency) in babies and how it has changed over time.
  • Note your baby's current age and which age-specific patterns you are seeing.
  • Mention if your baby received an abnormal MCADD result on newborn screening — follow up for confirmatory testing and metabolic specialist referral.
  • Mention if your baby with MCADD is a picky eater or frequently refuses to eat, making it hard to meet fasting guidelines.
  • Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
  • Bring a list of any questions or observations you want to discuss at the appointment.

What Should You Do?

When to take action

Probably normal when...
  • Your baby's newborn screening came back normal for MCADD
  • Your baby with MCADD is feeding well, growing normally, and has had no metabolic crises
  • An initial positive screen was followed by confirmatory testing that showed the baby does not have MCADD — some variants detected on screening are benign
  • Your child with MCADD is eating regularly, following the fasting guidelines, and has an emergency plan in place
Mention at your next visit when...
  • Your baby received an abnormal MCADD result on newborn screening — follow up for confirmatory testing and metabolic specialist referral
  • Your baby with MCADD is a picky eater or frequently refuses to eat, making it hard to meet fasting guidelines
  • You are unsure about the safe fasting duration for your child's age or how to manage during illness
Act now when...
  • Your baby with MCADD is ill and has not been able to eat for more than 4 hours (infants) or 6-8 hours (older babies) — go to the emergency room for IV glucose with your metabolic emergency letter
  • Your baby with MCADD becomes lethargic, unusually sleepy, difficult to wake, or has seizures — call 911 and tell them your child has a metabolic disorder
  • Your baby with MCADD is vomiting and cannot keep any food or fluids down — do not wait for the next scheduled feeding, seek emergency care immediately
  • An undiagnosed newborn becomes extremely lethargic, is difficult to wake for feedings, or has seizures in the first days of life before newborn screening results return

What You Can Do at Home

  • Keep track of when you notice mcadd (medium-chain acyl-coa dehydrogenase deficiency) in babies — noting the time of day, duration, and any triggers can help your pediatrician.
  • Remember that your baby's newborn screening came back normal for MCADD — this is generally within the range of normal.
  • At 0-1 week, focus on observation rather than intervention unless your pediatrician advises otherwise.
  • Follow any care instructions from your pediatrician. Keep a written log of symptoms to bring to appointments.
  • While monitoring at home, seek immediate care if your baby with MCADD is ill and has not been able to eat for more than 4 hours (infants) or 6-8 hours (older babies) — go to the emergency room for IV glucose with your metabolic emergency letter.

Abnormal Newborn Screening Results

An abnormal or positive newborn screening result means that further testing is needed, not that your baby definitely has a condition. Most positive screens turn out to be false positives after confirmatory testing. Newborn screening tests are intentionally sensitive to avoid missing any affected babies, so follow-up testing is essential to determine whether the result is a true positive.

Newborn Low Blood Sugar (Hypoglycemia)

Neonatal hypoglycemia (low blood sugar) is common in the first hours and days of life, especially in babies who are large or small for gestational age, premature, born to mothers with diabetes, or stressed during delivery. Mild hypoglycemia often responds to frequent feeding. More significant or persistent hypoglycemia may require IV glucose treatment. Early and frequent feeding is the best prevention.

Milestone

Month-by-Month Development

Detailed monthly development guides from birth through 24 months.

Guide

When to Call the Doctor

General guide on when to call the pediatrician, visit urgent care, or go to the ER.

Frequently asked questions

Is mcadd (medium-chain acyl-coa dehydrogenase deficiency) in babies normal?
MCADD (medium-chain acyl-CoA dehydrogenase deficiency) is the most common fatty acid oxidation disorder, affecting approximately 1 in 15,000 to 20,000 births. Babies with MCADD cannot properly break down medium-chain fats for energy during periods of fasting or illness. This can lead to dangerously low blood sugar (hypoglycemia), lethargy, seizures, and liver failure. MCADD is detected through newborn screening, and with proper management — primarily avoiding prolonged fasting — children with MCADD can live completely healthy lives.
When should I call the doctor about mcadd (medium-chain acyl-coa dehydrogenase deficiency) in babies?
Your baby with MCADD is ill and has not been able to eat for more than 4 hours (infants) or 6-8 hours (older babies) — go to the emergency room for IV glucose with your metabolic emergency letter Your baby with MCADD becomes lethargic, unusually sleepy, difficult to wake, or has seizures — call 911 and tell them your child has a metabolic disorder Your baby with MCADD is vomiting and cannot keep any food or fluids down — do not wait for the next scheduled feeding, seek emergency care immediately
When is mcadd (medium-chain acyl-coa dehydrogenase deficiency) in babies normal?
Your baby's newborn screening came back normal for MCADD Your baby with MCADD is feeding well, growing normally, and has had no metabolic crises An initial positive screen was followed by confirmatory testing that showed the baby does not have MCADD — some variants detected on screening are benign
What causes mcadd (medium-chain acyl-coa dehydrogenase deficiency) in babies?
MCADD (medium-chain acyl-CoA dehydrogenase deficiency) is the most common fatty acid oxidation disorder, affecting approximately 1 in 15,000 to 20,000 births. Babies with MCADD cannot properly break down medium-chain fats for energy during periods of fasting or illness. This can lead to dangerously low blood sugar (hypoglycemia), lethargy, seizures, and liver failure. MCADD is detected through newborn screening, and with proper management — primarily avoiding prolonged fasting — children with MCADD can live completely healthy lives. Common explanations include: Your baby's newborn screening came back normal for MCADD. Your baby with MCADD is feeding well, growing normally, and has had no metabolic crises.
What should I mention to my pediatrician about mcadd (medium-chain acyl-coa dehydrogenase deficiency) in babies?
You should mention mcadd (medium-chain acyl-coa dehydrogenase deficiency) in babies at your next visit if: Your baby received an abnormal MCADD result on newborn screening — follow up for confirmatory testing and metabolic specialist referral. Your baby with MCADD is a picky eater or frequently refuses to eat, making it hard to meet fasting guidelines. You are unsure about the safe fasting duration for your child's age or how to manage during illness.
Is mcadd (medium-chain acyl-coa dehydrogenase deficiency) in babies normal at 0-1 week?
Newborns with MCADD are at immediate risk because they have limited energy stores and must eat frequently. Before newborn screening results are available, undiagnosed babies can develop a metabolic crisis if they go too long without feeding. This is why it is important for all newborns to feed every 2-3 hours in the first days of life. If newborn screening detects MCADD, your baby's medical team will counsel you on safe fasting intervals and create an emergency plan.
Is mcadd (medium-chain acyl-coa dehydrogenase deficiency) in babies normal at 1-6 months?
Babies diagnosed with MCADD through newborn screening should not go more than 4 hours without feeding. Breastfeeding and formula feeding are both safe. No special formula or dietary changes are needed — the key is preventing prolonged fasting. During illness, even minor ones like colds with decreased appetite, extra vigilance is required to ensure adequate calorie intake. Your metabolic team will provide a sick-day emergency letter to carry at all times and may recommend a cornstarch-based supplement for emergency use.
Should I go to the ER for mcadd (medium-chain acyl-coa dehydrogenase deficiency) in babies?
Seek emergency care if your baby with MCADD is ill and has not been able to eat for more than 4 hours (infants) or 6-8 hours (older babies) — go to the emergency room for IV glucose with your metabolic emergency letter, or if your baby with MCADD becomes lethargic, unusually sleepy, difficult to wake, or has seizures — call 911 and tell them your child has a metabolic disorder. When in doubt, call your pediatrician's after-hours line for guidance.
Does mcadd (medium-chain acyl-coa dehydrogenase deficiency) in babies go away on its own?
In many cases, mcadd (medium-chain acyl-coa dehydrogenase deficiency) in babies resolves on its own, especially when your baby's newborn screening came back normal for MCADD. By Older children and adults, with ongoing awareness of fasting limits and proper sick-day management, children and adults with MCADD lead normal, healthy lives. Most learn to self-manage by recognizing early signs of low blood sugar (irritability, shakiness, pallor) and eating promptly. Exercise management may be discussed, as prolonged intense exercise can also deplete energy stores. MCADD is a lifelong condition but does not limit life expectancy when properly managed.
NIHHRSAACMG

References

  1. [1]National Library of Medicine. Medium-Chain Acyl-CoA Dehydrogenase Deficiency. MedlinePlus Genetics, 2023. NIH
  2. [2]Health Resources and Services Administration. MCADD Fact Sheet. Baby's First Test, 2023. HRSA
  3. [3]American College of Medical Genetics. ACT Sheet: Elevated C8/C8:C10 Acylcarnitine. ACMG, 2023. ACMG

Doctor Visit Checklist

Bring this checklist to your next pediatrician visit to discuss MCADD (Medium-Chain Acyl-CoA Dehydrogenase Deficiency) in Babies.

Things to mention

  • Describe when you first noticed mcadd (medium-chain acyl-coa dehydrogenase deficiency) in babies and how it has changed over time.
  • Note your baby's current age and which age-specific patterns you are seeing.
  • Mention if your baby received an abnormal MCADD result on newborn screening — follow up for confirmatory testing and metabolic specialist referral.
  • Mention if your baby with MCADD is a picky eater or frequently refuses to eat, making it hard to meet fasting guidelines.
  • Let your doctor know if you have noticed any related concerns, such as changes in feeding, sleep, or movement patterns.
  • Bring a list of any questions or observations you want to discuss at the appointment.

Observations to share

  • Your baby received an abnormal MCADD result on newborn screening — follow up for confirmatory testing and metabolic specialist referral
  • Your baby with MCADD is a picky eater or frequently refuses to eat, making it hard to meet fasting guidelines
  • You are unsure about the safe fasting duration for your child's age or how to manage during illness

Urgent signs to report immediately

  • Your baby with MCADD is ill and has not been able to eat for more than 4 hours (infants) or 6-8 hours (older babies) — go to the emergency room for IV glucose with your metabolic emergency letter
  • Your baby with MCADD becomes lethargic, unusually sleepy, difficult to wake, or has seizures — call 911 and tell them your child has a metabolic disorder
  • Your baby with MCADD is vomiting and cannot keep any food or fluids down — do not wait for the next scheduled feeding, seek emergency care immediately

My notes

From ismybabyalright.com — free, evidence-based baby health guides

All content follows our editorial policy and is reviewed against published clinical guidelines.

2,705 evidence-based guides6 authoritative medical sources5 medical advisory board members

Related Resources

Well-Baby Visit PrepEmergency ContactsBaby Tracker

Bottom line

Most cases of mcadd (medium-chain acyl-coa dehydrogenase deficiency) in babies are normal. Talk to your pediatrician if your baby with mcadd is ill and has not been able to eat for more than 4 hours (infants) or 6-8 hours (older babies) — go to the emergency room for iv glucose with your metabolic emergency letter.

Trust your instincts. If something feels wrong, reach out to your pediatrician. Worrying about your baby means you care — that is a good thing.

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Newborn Low Blood Sugar (Hypoglycemia)

Neonatal hypoglycemia (low blood sugar) is common in the first hours and days of life, especially in babies who are large or small for gestational age, premature, born to mothers with diabetes, or stressed during delivery. Mild hypoglycemia often responds to frequent feeding. More significant or persistent hypoglycemia may require IV glucose treatment. Early and frequent feeding is the best prevention.

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