The F351 - rPen a 1 Shrimp (recombinant, tropomyosin) Single Trophallergen test is used to detect specific IgE antibodies in a person's blood against Pen a 1, a recombinant form of tropomyosin found in shrimp. Tropomyosin is a protein involved in muscle contraction and is a common allergen in seafood, particularly shrimp.