Given that standard oncology care relies on sCr values and eGFR, the kidney filtering function is likely often overestimated, which can result in an increased incidence of delayed MTX excretion and subsequent toxicity. Therefore, mGFR may provide an optimal method to more accurately determine kidney filtering function and thereby allow prediction of which ALL patients will develop delayed MTX excretion and/or toxicity. The utility of mGFR in predicting MTX excretion delay and/or toxicity has not been previously studied.