A person presenting to a doctor with symptoms of SMA will first have their medical history taken and a physical examination performed. The doctor may order an EMG (electromyography) or a muscle biopsy. A blood test for creatine kinase levels in the weakened muscles may also be requested.

If doctors suspect SMA based on clinical findings (based on your child's symptoms and other diagnostic studies), they may deem a genetic test necessary to confirm the diagnosis. This is because a genetic test is the most definitive way to diagnose SMA associated with chromosome 5, namely types 1-4 SMA. An SMA diagnosis is confirmed in 95% of cases through DNA testing identifying deletions. The remaining 5% of disorders may present as other damaging mutations.