A premature neonate in the ICU suspected of having an infection has blood drawn for class specific ...

Ans: B
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Serology samples are used to identify infectious organisms by measuring the levels of antibodies. The measurement of antibody titers has another advantage in that specific antibody types such as IgM and IgG are produced by the host during different phases of an infectious process. IgM-specific antibodies generally rise and fall during the acute phase of the disease, whereas the synthesis of the IgG class of antibodies increases during the acute phase and remains elevated until or beyond resolution. Measurements of class-specific antibodies are also useful in the diagnosis of congenital infections. IgM antibodies do not cross the placenta, but certain IgG antibodies are transferred passively from mother to child during the final trimester of gestation. Consequently, an elevated level of pathogen-specific IgM antibodies in the serum of a neonate must have originated from the child and therefore indicates congenital infection. A similarly increased IgG titer in the neonate does not differentiate congenital from maternal infection.