Adhesion of HbSS RBCs to immobilized ICAM-1 in vitro correlates clinically with HbF levels. (A) There is an inverse relationship between RBC adhesion to ICAM-1 and HbF level. The P value was based on 1-way ANOVA. (B) Subjects with higher HbF levels (using a previously defined ameliorative cutoff of 8.6%²² ) had significantly lower numbers of adherent RBCs compared with those with lower HbF levels. The horizontal lines represent the means; ‘‘n’’ represents the number of subjects. The Mann-Whitney nonparametric U test was used to calculate the P value in panel B. PCC, Pearson’s correlation coefficient.