Know Your Numbers: Understanding CK and VLCAD Deficiency
If you or your child lives with Very Long-Chain Acyl-CoA Dehydrogenase (VLCAD) deficiency, chances are you have heard the letters CK more than once.
Maybe you've seen CK listed on routine bloodwork. Maybe your metabolic team has ordered it during an illness or after concerns about muscle pain or weakness. Or maybe you've watched that number rise during an episode of rhabdomyolysis and wondered what exactly it was telling you.
But what actually is CK? Why can it become elevated? And why is it a number VLCAD families may become very familiar with?
Let’s break it down.
What Is CK and What Does an Elevated CK Mean?
Creatine kinase (CK), sometimes called creatine phosphokinase or CPK, is an enzyme that plays an important role in energy production. Most CK in the body is found in skeletal muscle, although it is also found in heart muscle and in smaller amounts in the brain.[1]
Normally, there is a small amount of CK in the bloodstream. When muscle or other CK-containing tissue is damaged, larger amounts of CK can leak from the cells into the blood. That makes a CK blood test one tool healthcare providers can use to help identify and monitor muscle injury.[1]
But there is something important to understand:
CK is not a VLCAD-specific test, and an elevated CK does not tell the whole story.
Many different circumstances can cause CK to rise. Physical activity, for example, can affect CK levels, and normal values can vary based on factors such as age, sex, muscle mass and activity.[1]
A CK result also cannot tell a healthcare provider by itself exactly where damage occurred or what caused it. Instead, healthcare teams may consider CK alongside symptoms, medical history, physical activity, other laboratory results and what was happening when the test was taken.[1]
For someone living with VLCAD, the important question isn't simply “Is my CK high?” but rather, “What does this result mean for me or my child in this situation?”
That's a conversation you should consisently have with your individual metabolic team.
Why Does CK Matter in VLCAD?
To understand the connection between VLCAD and CK, it helps to understand what happens when the body needs energy.
VLCAD deficiency affects the body's ability to break down certain long-chain fatty acids for energy. The VLCAD enzyme normally plays a role in mitochondrial fatty-acid oxidation, the process the body uses to turn long-chain fats into energy, particularly during times of fasting and increased physiologic stress.[2,3]
Dr. Jerry Vockley of UPMC Children's Hospital of Pittsburgh and the University of Pittsburgh has described long-chain fatty acid oxidation disorders as conditions involving both acute crises of energy production and chronic energy deficiency. These energy challenges can contribute to complications including hypoglycemia, cardiomyopathy, muscle disease and rhabdomyolysis.[3]
Think of the connection this way:
The body needs energy → muscles have significant energy demands → VLCAD makes accessing fat-derived energy more difficult → metabolic stress can place additional strain on muscle → muscle injury can release CK into the bloodstream.
GeneReviews identifies intermittent rhabdomyolysis, muscle cramps or pain, exercise intolerance and intermittent CK elevations among possible features of VLCAD deficiency. CK measurement is also included among recommended surveillance for individuals living with VLCAD.[2]
What Can Muscle Injury Look Like?
A CK number is only one piece of information. Sometimes, changes in how someone feels, moves or tolerates their normal activities may be the first indication that something is different.
Muscle pain or cramping and exercise intolerance are recognized muscle-related features of VLCAD, while symptoms associated with rhabdomyolysis can include muscle pain or cramping, weakness or unusual tiredness, and dark or tea-colored urine.[2,4]
Possible signs and symptoms can include:
Muscle or leg pain
Muscle cramps or aching
Muscle weakness
Feeling unusually or extremely tired
Difficulty tolerating normal physical activity or exercise
Dark, red, tea- or cola-colored urine
For younger children especially, recognizing muscle pain or weakness isn't always straightforward. A young child may not have the words to explain that their muscles hurt, their legs feel weak, or something simply doesn't feel right.
Instead, parents and caregivers may notice a change from their child's normal behavior, movement, gait or activity level. A child might suddenly not want to walk, ask to be carried, move differently or begin walking on their tiptoes when that isn't typical for them.
It is important to make a distinction here: tiptoe walking itself is not identified in the medical literature cited for this article as a recognized or diagnostic sign of elevated CK or rhabdomyolysis. However, a new or unusual change in the way someone walks or moves can still be valuable information to share with their metabolic team, particularly when it occurs with other symptoms or represents a noticeable change from that individual's normal.
You also cannot determine someone's CK level from symptoms alone. Symptoms can overlap with many other conditions, and CK can only be measured through blood testing.[1,4]
Every person living with VLCAD can present differently. Families should follow their individualized emergency or illness plan and talk with their metabolic team about the specific symptoms and changes they want them to watch for.
Understanding Rhabdomyolysis in VLCAD
Rhabdomyolysis, often shortened to “rhabdo,” occurs when damaged skeletal muscle breaks down and releases substances from those muscle cells into the bloodstream. CK can increase significantly when this muscle damage occurs.[1,4]
Recurrent episodes of rhabdomyolysis are a recognized complication of VLCAD deficiency.[2]
Research has also helped scientists better understand why exercise can create challenges for skeletal muscle in VLCAD.
A study examining exercise in individuals with VLCAD found altered energy balance in skeletal muscle during moderate exercise. The researchers concluded that muscle energy balance during exercise is disrupted in VLCAD, providing additional insight into vulnerability to exercise-associated rhabdomyolysis.[5]
The concern with rhabdomyolysis isn't limited to the muscles themselves. GeneReviews notes that acute rhabdomyolysis can result in myoglobinuria, which can put kidney function at risk.[2]
This is one reason changes in muscle symptoms and laboratory findings such as CK can become important pieces of information for a metabolic team evaluating someone with VLCAD.
There Isn't One “Magic Number”
When a CK result comes back, it's natural to immediately wonder:
Is this high? How high is too high? What does this mean?
Unfortunately, there isn't one CK number that means the same thing for every person or every situation.
CK levels can vary, and GeneReviews notes that individuals with VLCAD may experience intermittent CK elevations that return toward normal between episodes.[2]
Research involving people with VLCAD has also explored relationships between CK and other biochemical markers. A 2019 study of 26 individuals with confirmed VLCAD found an association between C14:1 acylcarnitine levels and CK, supporting the importance of considering multiple pieces of biochemical and clinical information rather than relying on one number alone.[7]
The number matters but so does the context.
Your metabolic team is the best resource for understanding what a particular CK result means for you or your child.
Why “Knowing Your Numbers” Still Matters
Knowing your numbers doesn't mean diagnosing a metabolic crisis yourself or making treatment decisions based on a lab result.
It means better understanding the information your healthcare team is using to care for you or your child.
If CK is something your metabolic team monitors, knowing why they're checking it, what can affect it and how the results fit into the bigger picture can make conversations about VLCAD care a little easier to navigate.
Some questions you may want to ask your metabolic team include:
Why do you monitor CK for me or my child?
What has our typical CK looked like over time?
What factors can affect a CK result?
How do symptoms influence how you interpret CK?
When might you repeat CK testing?
How does CK fit into our individualized emergency or illness plan?
What symptoms or changes do you want us to contact you about?
The answers won't necessarily be the same for every person living with VLCAD, and that's exactly why understanding your own numbers and individualized care plan matters.
What Research Is Teaching Us About VLCAD Muscle Health
Researchers are continuing to learn more about what happens inside the body in VLCAD, and the science may be more complex than energy deficiency alone.
Research from Dr. Jerry Vockley and colleagues at UPMC Children's Hospital of Pittsburgh and the University of Pittsburgh has explored the potential role of inflammation in VLCAD deficiency.
In a 2021 peer-reviewed study involving 18 individuals with VLCAD, researchers found evidence of increased inflammatory activity during both symptomatic and asymptomatic periods. The study also followed a patient with recurrent rhabdomyolysis-related hospitalizations and observed persistent inflammatory activity.[6]
The researchers suggested that inflammation may represent another physiologic component of VLCAD deficiency in addition to impaired energy metabolism.[6]
This does not mean inflammation has been proven to cause rhabdomyolysis in VLCAD, nor does the study establish a new treatment recommendation. The study was small as is often the case in rare disease research, and the authors emphasized the need for additional research.
But findings like these show why continued research matters.
Scientists are still learning about the biological processes involved in VLCAD, muscle health and rhabdomyolysis. A better understanding of those processes could ultimately help researchers explore new approaches to monitoring and managing the disease.
How Is CK Measured Today?
Today, a standard CK test requires a blood sample, which is analyzed to determine the amount of creatine kinase present in the blood.[1]
For VLCAD families, that may mean bloodwork during routine surveillance or additional testing when a healthcare team is concerned about muscle symptoms or metabolic stress. GeneReviews includes periodic CK measurement among recommended surveillance for individuals with VLCAD deficiency.[2]
Traditional blood testing provides healthcare professionals with information about CK at the time the blood sample was collected.
And that leads to an important question:
Could there someday be a better way to monitor changes in CK and muscle health?
That's a question that is especially important to us at Maddie's Spark Foundation.
Looking Toward the Future of CK Monitoring
Today, CK is measured through a blood test, providing a snapshot of what is happening at that moment. But what if families and healthcare teams had a better way to understand changes in CK over time?
That possibility is what inspired Maddie’s Spark Foundation’s Early SparCK Initiative.
Launched in 2026, the Early SparCK Initiative has a goal of raising $100,000 to provide funding support to Dr. Jerry Vockley and his research team at UPMC Children’s Hospital of Pittsburgh as they continue the development of an emerging at-home continuous CK monitoring and disease-management device and work toward moving the technology into clinical trials.
The hope is that this research could one day lead to a better way for individuals living with VLCAD and related LC-FAODs, their families, and healthcare teams to understand changes in CK and muscle health without relying solely on traditional laboratory blood draws.
There is still important research, development, and testing ahead, but helping move promising tools like this from the research lab toward clinical trials is exactly why the Early SparCK Initiative was created.
Knowledge Is One More Tool
Understanding CK won't tell you everything happening in the body, and a number should never replace the guidance of your metabolic team.
But understanding what CK measures, why it can change and why your healthcare team may monitor it can make one more part of this complicated rare disease a little easier to understand.
As researchers continue learning more about VLCAD, we hope that knowledge leads to better monitoring, better disease-management tools, better treatments and ultimately a better future for our VLCAD community.
At Maddie's Spark Foundation, we'll continue working to help families understand the research, ask informed questions and stay connected to the progress happening along the way. 💗✨
Important Medical Disclaimer
This article is intended for general educational and informational purposes only and is not medical advice. VLCAD deficiency can present differently from person to person, and CK results should be interpreted by qualified healthcare professionals in the context of an individual's symptoms, medical history, laboratory findings and personalized care plan. Always follow your individualized VLCAD emergency protocol and contact your metabolic physician or healthcare team with questions about symptoms, CK results, illness management or treatment decisions.
Sources & Footnotes
[1] National Library of Medicine. “Creatine Kinase.” MedlinePlus Medical Test. U.S. National Library of Medicine, National Institutes of Health. MedlinePlus — Creatine Kinase
[2] Leslie ND, Saenz-Ayala S. “Very Long-Chain Acyl-Coenzyme A Dehydrogenase Deficiency.” GeneReviews®. NCBI Bookshelf, National Library of Medicine. GeneReviews — VLCAD Deficiency
[3] Vockley J. “Long-chain fatty acid oxidation disorders and current management strategies.” American Journal of Managed Care. 2020;26(7 Suppl). Dr. Jerry Vockley, UPMC Children's Hospital of Pittsburgh and University of Pittsburgh. PMID: 32840329. PubMed — Vockley 2020
[4] Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. “Signs and Symptoms of Rhabdomyolysis.” CDC — Rhabdomyolysis Signs and Symptoms
[5] Diekman EF, et al. “Altered Energetics of Exercise Explain Risk of Rhabdomyolysis in Very Long-Chain Acyl-CoA Dehydrogenase Deficiency.” PLOS ONE. 2016;11. PMID: 26881790. PubMed — Diekman et al.
[6] Vallejo AN, Mroczkowski HJ, Michel JJ, et al.; Vockley J. “Pervasive inflammatory activation in patients with deficiency in very-long-chain acyl-CoA dehydrogenase (VLCADD).” Clinical & Translational Immunology. 2021;10(6). Research conducted through UPMC Children's Hospital of Pittsburgh and the University of Pittsburgh. PMID: 34194748. PubMed — Vallejo et al.
[7] “Clinical and biochemical outcome of patients with very long-chain acyl-CoA dehydrogenase deficiency.” Molecular Genetics and Metabolism. 2019;127(1):64–73. Journal article DOI
About the Early SparCK Initiative
The Early SparCK Initiative is a Maddie's Spark Foundation research initiative supporting work with Dr. Jerry Vockley and his research team at UPMC Children's Hospital of Pittsburgh to advance an emerging at-home CK monitoring and disease-management device for individuals living with VLCAD deficiency.
