A 29-year-old non-smoker man presents with sneezing, post-nasal drip, eye-watering, and an itch of his posterior pharynx. These symptoms tend to be worse in the spring and summer and have been bothering him since mid-April, about 1 month ago. His past medical history is remarkable only for mild asthma induced by being outdoors. He takes no regular medications but does take diphenhydramine on occasion. Most appropriate diagnostic test at this time is?

**Core Concept**
The patient's symptoms suggest a seasonal allergic reaction, likely allergic rhinitis, triggered by exposure to environmental allergens such as pollen. This condition is characterized by an overactive immune response to harmless substances, leading to the release of histamine and other chemical mediators, which cause the symptoms.

**Why the Correct Answer is Right**
The most relevant diagnostic test in this case is the skin prick test (SPT), which involves exposing a small amount of the suspected allergen to the patient's skin and observing the reaction. The SPT is a quick, non-invasive, and relatively painless procedure that can help identify specific allergens responsible for the patient's symptoms. This information is crucial for developing an effective treatment plan, which may include avoidance of the allergen, use of medications such as antihistamines or corticosteroids, or immunotherapy.

**Why Each Wrong Option is Incorrect**
**Option A:** Blood tests for IgE antibodies may be used to diagnose allergic conditions but are not the most appropriate test for diagnosing seasonal allergic rhinitis, as they may not accurately reflect the patient's symptoms.

**Option B:** Nasal endoscopy may be used to visualize the nasal passages and identify any anatomical abnormalities or inflammatory changes but is not a diagnostic test for allergies.

**Option C:** Chest X-ray may be used to evaluate respiratory symptoms in patients with asthma but is not relevant to diagnosing seasonal allergic rhinitis.

**Clinical Pearl / High-Yield Fact**
The patient's symptoms are worse in the spring and summer, and he has a history of mild asthma, suggesting that he may be allergic to pollen. A skin prick test or allergen extract challenge can help confirm this suspicion and guide treatment.

**Correct Answer:** C. Nasal endoscopy.

✓ Correct Answer: B. None, the diagnosis is based solely on the history and physical examination