Early rise in the "pitted" red cell count as a guide to susceptibility to infection in childhood sickle cell anaemia.

"Pitted" red cell counts (pit counts) were performed serially during a period of 18 months in 130 Jamaican children with homozygous sickle cell (SS) disease aged 0-4 years. Raised pit counts, defined as 10% or more "pitted" red cells, were present in 23% of the children at age 12 months, in 42% at age 24 months, and in 52% at age 36 months. Radioactive colloid spleen scans showed no splenic uptake in 11 children with palpable spleens and raised pit counts. Eight episodes of severe bacterial infection occurred in 7 children, all of whom had raised pit counts before (n = 6) or at the time of infection (n = 1). Of the 52 children with pit counts followed from age 12 months or younger, all 4 who developed severe infections had raised pit counts at or before age 12 months. Pit counts are a guide to susceptibility to severe infections in SS children. Children whose pit counts rise before age 12 months are at greater risk of subsequent infection; this may be related to loss of splenic function before first encounter with the infecting organism.