Paroxysmal nocturnal haemoglobinuria treatment with eculizumab is associated with a positive direct antiglobulin test

Paroxysmal nocturnal haemoglobinuria (PNH) is characterized by intravascular haemolysis with a negative direct antiglobulin test (DAT). Eculizumab is a humanized monoclonal antibody that inhibits complement component C5 and is approved for PNH treatment. Recent publications demonstrated that some patients with PNH develop a positive DAT during eculizumab treatment. These published clinical trials investigated a highly selected patient population. Therefore, it seems important to study this topic in a general PNH patient population with a longer follow-up.

We analysed haemolytic activity, RBC transfusion requirement, effect on DAT and ferritin levels in 41 patients with PNH before and during eculizumab therapy with a median follow-up of 24 months (range 1-63 months).

During eculizumab therapy, median LDH decreased (1657-258 U/l; P < 0·0001), while median haemoglobin increased (9·2-10·3 g/dl). Eighteen of 32 pts (56%) who previously required regular transfusions became transfusion independent. DAT was positive for C3d in 72·4% of 21 eculizumab-treated pts with available DAT. Ferritin levels increased (69-348 ng/ml, P < 0·0001). This increase was more pronounced in pts with ongoing transfusion dependency during eculizumab therapy.

Eculizumab therapy for PNH should be added to the list of possible causes for a positive DAT. Intravascular haemolysis was inhibited by eculizumab, but signs of extravascular haemolysis should be monitored. Because renal iron loss was stopped, eculizumab-treated pts can be prone to iron overload and therefore ferritin concentrations should be monitored closely.