This page reviews indications for CK testing in children ages 6 months to 5 years. If you see global delay, evaluate for muscle weakness. If you suspect muscle weakness, include a CK as part of your evaluation.
What is a CK (CPK)?
Creatine phosphokinase (CK) is an enzyme found mainly in the skeletal muscle, but also in the heart and brain. Higher-than-expected serum CK indicates leakage of CK through the muscle membrane, and suggests muscle damage either from cardiac or skeletal muscle. In children, elevated CK almost always reflects skeletal muscle damage.
Rationale for CK testing
A CK is a starting point in the evaluation of a child with motor delay, even if cognitive delay is more of a concern, and helps focus further testing and referrals.
CK testing is quick and inexpensive.
CK results can help clinicians differentiate between various disorders that cause weakness.
The CK can help distinguish between central (where there is normal CK) and peripheral (where CK may be elevated) causes of motor delay.
There are many peripheral neuromuscular conditions where the CK is always elevated from birth (e.g., in Duchenne and Becker muscular dystrophies, and in some of the congenital muscular dystrophies, and some limb girdle muscular dystrophies) and other conditions where CK is mildly elevated or normal (e,g., spinal muscular atrophy, neuropathies, and congenital myopathies).
Elevated CK warrants prompt referral to neurology. Normal CK does not rule out neuromuscular disease. A mildly elevated CK (1-2x normal) should be followed up.
Use of CK testing
A. In children with developmental delay:
Evaluate motor milestones in any child who has mild to moderate developmental delay of unknown etiology. (Note that some children with neuromuscular disorders have non-motor developmental delays; for example, delayed language. This may be the feature that first brings them to clinical attention.) If you have any concerns about motor development, include a CK in your screening process. If the CK is high, refer to neurology for consultation.
B. In children with motor delay:
Order a CK for a child who has unexplained gross motor delay. If the CK is high (≥3 x normal), refer to neurology for consultation.
Findings that should always trigger a CK include:
Signs of proximal muscle weakness, including:
Slipping through hands when held suspended
Inability to voluntarily flex neck when supine or head lag when pulled to sit
Difficulty rising from floor (including Gowers maneuver, full or modified)
Loss of motor milestones
Isolated gross motor delay without other developmental difficulties
ICD code for muscle weakness 728.87
Using this code is the best way to ensure reimbursement for CK testing