Vascepa is a prescription drug that contains the active ingredient icosapent ethyl, which is used to treat high levels of triglycerides in the blood. According to the sources provided, there is no information available on how Vascepa allergy is diagnosed. However, it is important to note that allergic reactions to Vascepa are rare.

If a person experiences symptoms of an allergic reaction such as hives, difficulty breathing, or swelling of the face, lips, tongue, or throat, they should seek immediate medical attention. In some cases, an allergist may perform skin testing or blood tests to diagnose an allergy to a medication, but it is unclear if this is applicable to Vascepa.

It is important to follow the instructions of a healthcare provider when taking Vascepa and to report any side effects or concerns. It is also important to inform the healthcare provider of any allergies or medical conditions before taking Vascepa.

Sources:
[1] https://www.drugpatentwatch.com/p/tradename/VASCEPA
[2] https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/202057s019lbl.pdf
[3] https://www.healthline.com/health/drugs/vascepa