The Dumas test can be used to determine the Total Protein (crude protein) in a sample, as well as the amount of Nitrogen. This can be used for nutrition labeling, as long as a protein claim is not being made.
The Dumas test does have limitations. Solvents, such as alcohol, and samples high in fats/oils can create fire hazards. The Kjeldahl method is a better choice for these types of samples.
The Dumas method, similar to Kjeldahl, is not a true protein test. Any nitrogen-containing ingredients or compounds can lead to inaccurate results.