The Aryl Sulfatase A test (often referred to as ARSA test, Aryl Sulphatase A (OS), or Arylsulphatase A, Leukocytes) is a diagnostic tool that measures the activity of the arylsulfatase A enzyme in the body. Its primary use is to diagnose or rule out Metachromatic Leukodystrophy (MLD), a rare, inherited neurological disorder