- Serum MTX >5 µmol/L 42 hours or later after the start of MTX infusion, or serum MTX >1 μmol/L 42 hours or later after the start of MTX infusion together with renal insufficiency, or serum MTX >0.4 µmol/L 48 hours or later after the start of MTX infusion together with renal insufficiency. Renal insufficiency was defined as serum creatinine >1.5 × the upper limit of normal (ULN) and/or oliguria (urine output < 500 mL/24 hours despite adequate hydration, diuretics and alkalinisation).