How Severe is Severe Enough? Organ Failure Rather Than Anemia Severity as a Potential Threshold for Complement...

Paroxysmal cold hemoglobinuria (PCH) is an acquired intravascular hemolytic anemia of young children that is usually self-limited. Two patients with PCH have previously been described in the medical literature to have received complement inhibition with eculizumab, an inhibitor of complement C5, and in both cases, the drug was given in the setting of organ failure. No criterion defines when the use of complement inhibition is warranted. We report a previously healthy 23-month-old boy with postviral PCH whose hemoglobin nadir of 2.7 g/dL, undetectable total hemolytic complement (CH50), and elevated soluble C5b-9 represent the most severe anemia among the three reported patients. Despite this laboratory severity, he remained hemodynamically stable with preserved renal function, never requiring vasoactive support or dialysis, and recovered with warmed transfusion and thermal protection after eculizumab was deferred. Our experience suggests that organ failure, rather than anemia or hemolysis severity alone, may be a more clinically meaningful indicator for escalation to complement inhibition.