In reply

Abstract

The main focus of our article was to validate the Modification of Diet in Renal Disease (MDRD) formula in a Norwegian population, and we found that recalibration of the serum creatinine assay reduced the negative bias of this formula in the normal and near-normal glomerular filtration rate (GFR) range.1 Dr. Lhotta suggests that tubular secretion of creatinine might also contribute to negative bias in the near-normal GFR range. All formulae tested in our article showed this bias, and when exploring the data of the original MDRD article the same bias occurs,2 so this is a general problem.