Allergic rhinitis is an increasingly common disease, with a prevalence of at least 10% to 25% in the United States. Diagnostic allergy tests, such as skin tests and in vitro tests, can assist clinicians in determining whether nasal symptoms are allergic in origin. In addition, safe and effective medications are available to treat allergic rhinitis. The initial strategy should be to determine whether patients should undergo diagnostic testing or receive empirical treatment. This paper reviews the test characteristics of the history, skin tests, and in vitro tests in diagnosing allergic rhinitis from the perspective of decision thresholds. A combination of pertinent medical history features in a practice with a high baseline prevalence of allergic rhinitis justifies the common practice of empirical treatment since allergy medication has minimal toxicity and side effects. The situation is more complex when the patient needs a diagnostic test, because reported sensitivities and specificities of skin tests and in vitro tests vary widely. As a result, it is difficult to calculate the post-test probability of allergic rhinitis with any confidence. The decision to initiate diagnostic testing must rely on clinical judgment to select patients who would benefit most from determining their allergic status while minimizing unnecessary testing and medications. Diagnosing allergy to a specific antigen allows patients to avoid the allergen and makes them candidates for allergen immunotherapy, which can decrease the need for medications.