What is the most likely cause of elevated serum IgG levels in a patient with isolated liver test abnormalities?

Elevated serum IgG levels in the context of isolated liver test abnormalities are most commonly associated with autoimmune disorders. This is primarily because autoimmune conditions, such as autoimmune hepatitis, typically lead to the production of antibodies against the body's tissue. In autoimmune hepatitis, for example, IgG levels can rise as the immune system becomes activated against liver antigens, resulting in liver inflammation and dysfunction.

In cases of chronic infections, malignancy, or metabolic syndrome, while they can also affect liver function tests, they do not typically result in isolated elevations of IgG to the same degree or under similar conditions as autoimmune processes. For instance, although certain viral infections can cause liver abnormalities, they may not lead to elevated IgG levels unless there is a specific autoimmune response triggered, which is less common.

Thus, when considering the combination of isolated liver test abnormalities and elevated serum IgG, autoimmune disorders are the most likely explanation due to their direct impact on antibody production in response to liver inflammation.