KM estimates of the probability of abnormal TCDI reversion on hydroxyurea. (A) KM estimates in the 46 patients. (B) KM estimates depending on the baseline reticulocyte count of <400 × 10⁹/L or ≥400 × 10⁹/L recorded before age 3 years. The KM-estimated cumulative risk of reversion in patients on hydroxyurea was 19.2% (95% CI, 7-31.4) at 1 year and 27.4% (95% CI, 13.2-41.6) at 2 years.