Is there one best test to diagnose duchenne muscular dystrophy?

A genetic test. Blood can be drawn for dna testing for the muscular dystrophy gene. That's the best test.
Serum CK. Serum ck is elevated in duchenne muscular dystrophy. This is a simple/common blood test. The polymerase chain reaction (pcr) test for the dystrophin gene confirms the diagnosis. If the PCR is inconclusive a muscle biopsy may follow.

Related Questions

How does duchenne muscular dystrophy affect the body?

See below. It is caused by an alteration (mutation) in a gene, called the dmd gene that can be inherited in families in an x-linked recessive fashion, but it often occurs in people from families without a known family history of the condition. Individuals who have dmd have progressive loss of muscle function and weakness, which begins in the lower limbs.