Cystatin C is a kidney function marker that was more strongly associated with methotrexate clearance than serum creatinine in adults with lymphoma. Including cystatin C in kidney function estimates improved the prediction of methotrexate elimination and supports its use in monitoring during therapy.

Measuring an early methotrexate concentration (4 h after the start of the infusion) helped predict acute kidney injury in patients receiving 3.5 g/m2 of methotrexate (but not in those receiving 8 g/m2), highlighting the value of an early sample as a tool to identify at-risk patients and support proactive care to prevent kidney injury and other complications.