Bactericidal screening test for late complement component deficiencies or defects.

Congenital complement deficiency has been described in disseminated Neisseria infections. Its occurrences in humans with other kinds of infections have not been described. In the past, CH50 determinations have been used to detect these deficiencies, but this procedure is time consuming and cumbersome. A method of determining the presence of late component deficiencies or defects is described which is easy and inexpensive to perform. An agar pour plate with a serum-sensitive Escherichia coli strain is made, and 2.5-mm wells are put in the agar. Unknown fresh sera are used to fill the wells. An absence of a zone of bacterial growth inhibition around the well after incubation at 37 degrees C overnight indicates a late component defect or deficiency in the test serum. By applying this assay to 35 selected patients, four deficient patients were identified. One had a congenital C5 deficiency and three had C6 deficidencies. It is suggested that the assay be used as a screening test to study the relationship between congenital complement deficiencies and various kinds of infections, especially those caused by organisms which are partially serum sensitive.