Urinary N-acetyl-beta-D-glucosaminidase activity in leukaemic children during high-dose methotrexate therapy

Urinary N-acetyl-beta-D-glucosaminidase (NAG-ase) activity is a very sensitive parameter of kidney proximal tubular damage. Using urinary NAG-ase activity/urinary creatinine as the NAG index, the serum methotrexate (MTX) level and urinary pH were investigated simultaneously. These parameters were measured in 17 leukaemic children. During MTX treatment, NAG indices were normal in 5 children and only slightly elevated occasionally in 9 patients. Among them, transiently high serum MTX levels (Patient A) or low urinary pH (Patient B) were accompanied by high NAG indices. MTX toxicity has been diagnosed in 3 cases, when permanently high NAG indices were in accordance with other clinical signs.