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.