Methods
Patients and samples
pH was assessed on 116 urine samples from 4 patients receiving high-dose MTX treatment using the Clinitek Status (Siemens Healthcare Diagnostics, Tarrytown NY) dipstick analyzer and an Accumet AR15 or XL15 pH meter (Fischer Scientific, Pittsburgh PA). pH meters were calibrated daily with buffers at pH 4.0, 7.0 and 10.0, while two levels of external daily quality control were performed on the Clinitek. pH was also assessed on 50 normal-colored urine samples with pH values between 5.5 and 9.0 received from areas of the hospital where patients were not receiving MTX therapy. The study design was approved by the Institutional Review Board.