Which of the following is a characteristic of mild blue baby syndrome?

Mild blue baby syndrome, also known as methemoglobinemia, involves an increased level of methemoglobin in the blood, which can reduce the blood's ability to carry oxygen and lead to a bluish coloration of the skin, particularly in infants. In some cases, treatment with methylene blue is indicated because it acts as a reducing agent that can convert methemoglobin back to hemoglobin, thereby improving oxygenation.

The presence of other options does not relate to the specific characteristics of mild blue baby syndrome. High fever, for instance, is not a typical sign; rather, it usually signifies an infection or inflammatory response. Severe jaundice, which involves high levels of bilirubin in the blood resulting in yellowing of the skin and eyes, is not associated with this condition and points to liver or blood disorders. Adverse reactions to vaccines may occur generally in children but are not characteristic of mild blue baby syndrome specifically. Therefore, the potential need for methylene blue treatment is the accurate characteristic associated with this syndrome.