False Elevation in Serum Creatinine Levels

To the Editor.— Flucytosine causes a falsely elevated serum creatinine measurement when an analytic method using creatinine iminohydrolase is employed.1This enzymatic assay is being introduced into many hospital laboratories, replacing systems with which flucytosine did not interfere. Report of a Case.— A 53-year-old man with alcoholic cirrhosis and cryptococcal meningitis was receiving therapy with amphotericin B (0.3 mg/kg/day) and flucytosine (150 mg/kg/day). His serum creatinine level, which was 1.0 mg/dL prior to drug therapy, rose to 3.2 mg/dL on the fourth day of therapy. The dosing regimen was altered because of the possibility of amphotericin-related renal dysfunction and the consequent possibility of bone marrow toxic reaction from flucytosine. Serum creatinine values then fluctuated on a daily basis, with a high of 6.3 mg/dL, a low of 1.1 mg/dL, and a mean of 3.5 mg/dL. It was discovered that creatininemeasurements were being determined on a Kodak Ektachem 400