Final answer:
The nurse practitioner should check the patient's Immunoglobulin E (IgE) levels.
Step-by-step explanation:
The patient's symptoms of wheezing, shortness of breath, and fatigue after mowing the lawn and gardening suggest an allergic reaction. In this case, the nurse practitioner should check the patient's Immunoglobulin E (IgE) levels. IgE is responsible for allergic reactions and can help determine if the patient is experiencing an allergic response to something in the environment, such as pollen or grass.