Serious haemolysis is identified by serum LDH levels greater than the pre-treatment level, along with any of the following: greater than 25% absolute decrease in PNH clone size (in the absence of dilution due to transfusion) in one week or less; a haemoglobin level of < 5 gm/dL or a decrease of > 4 gm/dL in one week or less; angina; change in mental status; a 50% increase in serum creatinine level; or thrombosis.