Question 2: At what age do children with SCA become functionally asplenic?
The spleen is important in the removal of encapsulated organisms in young children who have not developed antibodies to pathogens such as Streptococcus pneumoniae, Haemophilus influenzae, and Salmonella species.1 Early studies regarding splenic dysfunction involved radio-labeled technetium-99 and demonstrated diminished uptake within the first six to 12 months of life, suggesting splenic dysfunction.2 While this study showed diminished uptake of a radio-labeled substance, it still didn’t necessarily mean that the child demonstrated either total or clinically significant dysfunction of the spleen. A later prospective study included 694 children with sickle cell disease at 19 U.S. pediatric sickle cell centers and suggested poor splenic function in 94 percent of sickle cell anemia (SCA) patients by 5 years of age; 28 percent of children had poor splenic function at 1 year of age and the authors noted that initial splenic dysfunction rose sharply after 6 months of age.3 While functional asplenia may occur by 5 years of age, these studies suggest that splenic dysfunction begins as early as the first year of life.
But what if we could measure a patient’s spleen via ultrasound in the emergency department (ED) to guide specific patient care? Is there a correlation? Practitioners have looked at splenic size on ultrasound and its association with splenic dysfunction. A multi-institutional, randomized, double-blinded, placebo-controlled trial (the BABY HUG trial) evaluated spleen size as well as serum labs and splenic dye uptake of technetium-labeled sulfur colloid.4 This study served to report baseline data for a future randomized controlled trial on hydroxyurea in patients with SCA. A total of 203 infants, ranging from 7.5 to 18 months of age, were evaluated for baseline data. Of these children, 12 percent had normal uptake, 74 percent had present but decreased uptake, and 14 percent had absent uptake. There was no correlation between spleen volume and function assessed by dye study, suggesting that that measurement of the spleen is not a method that can be utilized for assessment of splenic dysfunction. It also suggests that there is a portion of infants and toddlers that already demonstrate very poor splenic function even at this young age. Another similar study of 100 children aged 7 months to 16 years evaluated ultrasound-measured spleen size and splenic function.5 While the splenic sizes varied between these two studies in regard to the age of splenic auto-infarction, they found that spleen size did not predict splenic function. This would suggest that measuring the spleen via ultrasound is not a reliable method to predict splenic function in the ED setting.