PlGF concentration is increased in plasma of subjects with SCD at steady state and correlates with incidence of VOCs. PlGF concentration was determined on cell-free heparinized plasma from SCD subjects and from healthy controls using ELISA (y-axis). Subjects were classified as mild and severe disease based on the incidence of severe VOCs per year (x-axis). Each point (♦) represents average values of duplicate samples from individual subjects. Mean values are represented as thick black bars, with values adjacent to the symbol. Medians represented as ○. Error bars represent SEM.