• Written informed consent from patients aged ≥ 18 years before any evaluation is performed.

• Written informed consent from parents or legal guardian and assent from minors aged under 18 years before any evaluation is performed.

• Recurrent acute pericarditis during the acute phase of the disease. The diagnosis of pericarditis is based on the presence of at least two of the following criteria: typical pericarditic chest pain (acute and pleuritic, worsened by positional changes or breathing), pericardial friction rub, diffuse ST segment elevation or PR depressions not previously reported, and pericardial effusion.

• Post-cardiac injury pericarditis (e.g., post-cardiac surgery) that is new or worsening. Recurrence is diagnosed based on the same criteria.

⁃ In all patients, the previous history of CRP values should be known to distinguish individuals with inflammatory forms (characterized by significantly elevated CRP values in the clinical history) from those with pericarditis and normal or near-normal CRP levels (clinical history of normal or at most less than 2 times the normal value).

⁃ The acute phase of the disease is defined as follows: for pericarditis forms with elevated CRP, the presence of a CRP that is at least double the normal value of the test. For forms with normal CRP, it is based on clinical judgment, as there are no other recognized and validated criteria.