Relationship between complement inhibition with eculizumab and various hemolytic parameters and symptoms during a transient breakthrough in serum-complement activity. Urine color, symptoms, biochemical parameters of hemolysis, PK, and PD were assessed during a 14-day eculizumab-dosing interval in a patient with a transient breakthrough in serum hemolytic activity. Eculizumab was administered on day 0 after assay samples were collected. A urine colorimetric score of 6 or greater was considered abnormal (hemoglobinuria). Levels of the hemolytic markers LDH and AST are shown (IU/L). Eculizumab serum concentrations (PK, μg/mL) of ≥ 35 μg/mL were sufficient to maintain a serum hemolytic activity (PD, % serum hemolytic activity) of ≤ 20%, a value known to represent complete complement blockade. The eculizumab-dosing interval was reduced to 12 days between visits 5 and 9. Urine row presents colorimetric scores. — indicates not determined. ^*Dose of eculizumab.