Which abbreviation refers to an amino acid-based formula for patients with food allergies?

The abbreviation that refers to an amino acid-based formula for patients with food allergies is "AA." Amino acid-based formulas are specifically designed for individuals who cannot tolerate intact proteins, typically due to allergies or certain gastrointestinal conditions. These formulas provide essential nutrients in the form of free amino acids, which are the building blocks of proteins.

Amino acid formulas are particularly beneficial for patients with conditions such as protein intolerance, cow's milk protein allergy, or other food allergies, as they minimize the risk of allergic reactions that can occur with whole proteins. This makes "AA" the most appropriate choice in this context, as it directly denotes the nature of the formula being composed of amino acids, catering to the dietary needs of these patients.

Other options do not specifically denote an amino acid-based formula. PPN (Partial Parenteral Nutrition) refers to a method of delivering nutrients intravenously but does not specify amino acids. TPN (Total Parenteral Nutrition) is a comprehensive intravenous nutrition solution but may contain whole proteins rather than just amino acids. ENS (Enteral Nutrition Support) typically represents nutrition delivered via the gastrointestinal tract, which could include whole proteins or intact formulas.