Impact of a new assay for measuring serum creatinine levels on carboplatin dosing

PURPOSE: The impact of converting to the isotope dilution mass spectrometry (IDMS)-traceable serum creatinine (SCr) assay for determining the calculated and delivered dose of carboplatin was studied. METHODS: A single-center, retrospective, observational chart review of adult patients who received a dose of carboplatin within one month before and after implementation of the IDMS-traceable SCr assay was conducted using information available in medical records and chemotherapy orders. Patient-specific data were collected and used to calculate a carboplatin dose before and after the SCr assay change using the Cockcroft-Gault equation, with the Calvert et al. formula used to calculate the carboplatin dose based on the target area under the concentration-time curve in the chemotherapy order forms. The primary outcome was the difference in calculated carboplatin dose, assessed as the percent difference between the mean carboplatin dose before and after the assay change. Results Fifty-six patients were included in the data analysis. The mean calculated carboplatin dose was 9.6% greater when the IDMS-traceable assay was used compared with the previous institutional standard enzymatic assay. This difference was statistically significant (p < 0.005). Nearly 50% of patients received a dose of carboplatin that was increased by >10% compared with the dose received before conversion to the IDMS-traceable assay for SCr measurement. CONCLUSION: After implementation of the IDMS-traceable assay, the mean calculated carboplatin dose was 9.6% larger than before implementation, and nearly 50% of patients received a dose of carboplatin that was increased by greater than 10% compared with the dose received before the assay change.