What is one of the four categories used for diagnosing rheumatoid arthritis according to the new classification criteria?

Multiple joint involvement is a key factor in the diagnosis of rheumatoid arthritis according to the new classification criteria. This condition is characterized by polyarthritis, which typically affects multiple joints symmetrically, often including small joints such as those in the hands and feet. The presence of multiple joints involved helps in establishing the likelihood of rheumatoid arthritis versus other forms of arthritis, which may affect fewer joints or be asymmetrical in presentation.

In the context of the classification criteria, the degree of joint involvement can influence the categorization of the disease's severity and help guide treatment options. The classification criteria prioritize objective findings, such as multiple joint involvement, to facilitate accurate diagnosis and subsequent management of the condition in clinical practice.

In contrast, the other options, while they may be relevant to the overall clinical picture, do not hold the same weight in the formal classification criteria. For instance, while joint swelling can be a symptom, it alone is not sufficient for diagnosis without considering other criteria. A family history could provide context but is not a definitive classification criterion on its own. The presence of fever is more indicative of an inflammatory response, which isn't a primary factor in identifying rheumatoid arthritis specifically.