Endotoxin levels in immunocompromised children with fever.

Febrile episodes for which no cause can be found are common in immunocompromised children. We postulated that circulating endotoxin, a known pyrogen, might be responsible for some of these episodes in the absence of documented infection. Plasma endotoxin levels were assayed using a recently developed Limulus amebocyte lysate assay enhanced in sensitivity and objectivity by the addition of a chromogenic substrate. Eighty-seven plasma endotoxin determinations were made in 36 immunocompromised children with fever. Convalescent endotoxin levels and levels in normal children were also obtained. It was concluded that a plasma endotoxin level of 35 pg (0.10 EU)/ml constitutes the upper limit of normal in children. Five children (14%) had elevated endotoxin levels in the course of the febrile episodes, in the absence of bacteremia or clinically diagnosed infection. In each case, the levels returned to normal during convalescence. It is concluded that endotoxemia is a possible cause or contributing cause of unexplained fever in immunocompromised children.