Wheatgrass in its purest form is gluten free, according to About.com. The type of gluten that affects people with gluten sensitivity or celiac disease is the grain or seed that is produced by rye, barley and wheat plants.
Wheatgrass is completely gluten free if it was correctly harvested and only the grass is eaten. However, people with gluten sensitivity or celiac disease have to be careful not to eat any of the seeds that are produced by the grass if it's not harvested at the right time. The U.S. Food and Drug Administration allows companies to put the gluten-free label on foods that have less than 20 parts per million of gluten.
While wheatgrass is gluten free in its purest form, the way the grass is produced plays a factor because gluten is found in the grass' seeds. Also, if manufacturers process the wheatgrass on the same equipment that gluten products are produced, the wheatgrass may pick up traces of gluten. It's generally recommended to avoid eating any kind of wheatgrass that isn't labeled gluten free. If a gluten-sensitive person is unsure if wheatgrass is completely gluten free, there are other green vegetables that provide roughly the same benefits, such as spinach.