Comparing two measures of creatinine clearance: an application of errors-in-variables and bootstrap techniques

Two indices of creatinine clearance tan index of kidney function) are compa red on a group of cancer patients who underwent chemotherapy with a potenti ally nephrotoxic drug. The standard index, measured creatinine clearance MC C, is cumbersome to use; whereas the more convenient alternative, estimated creatinine clearance ECC, has not yet been conclusively evaluated on cance r patients. We conclude that under certain clinical conditions ECC and MCC are identically calibrated for males, but not for females, and we obtain es timated true and false positive rates for assessing the use of ECC instead of MCC as a diagnostic tool. We use a model that is formally equivalent to an errors-in-variables model with (unbalanced) repeated observations and co rrelated measurement errors. The bootstrap is used to obtain standard error s and confidence limits.