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Diagnosing a cold or the flu (influenza) usually begins with a physician performing a thorough medical history that includes a description of symptoms, as well as their duration and severity. A physical examination is often necessary. For example, the presence of nasal secretions can be obvious upon examination and may indicate the presence of a viral infection. Examination of the ears, nose or throat may indicate the presence of a cold or the flu – or may indicate the presence of another condition responsible for the symptoms. In the latter case, additional tests may be necessary to rule out other conditions (e.g., strep throat, asthma, allergies).

Additional tests that can rule out other conditions may include a throat culture, in which the physician uses a long cotton swab to collect a tiny tissue sample from inside the throat. A nasal smear (analysis of nasal excretions under a microscope) or blood tests may also be used. Examination of the ears during the physical examination can help identify an ear infection (otitis media). Tests may be used to identify complications of a cold or the flu, such as sinusitis and pneumonia.