Serum IgM in diagnosis of infection in the newborn.

Serum IgM levels were determined at weekly intervals from birth in 100 normal low birthweight and 100 normal birthweight infants during the first 4 weeks of life. The dynamics of serum IgM was also studied in 36 newborn infants with different types of infection and in 19 infants with probable infection. The behaviour of serum IgM in the infants with systemic infection and also in those suffering from superficial infection with systemic symptoms was significantly different from the normal. Serum IgM rose within two days of appearance of symptoms and the rise persisted as long as the infection was `active'. With the eradication of infection the IgM level tended to fall. This characteristic dynamic pattern of serum IgM may be of considerable help in the diagnosis of neonatal infection, especially the clinically inapparent and atypical varieties that may have serious sequelae later in life.