Concerns have been raised within the nuclear medicine field about the accuracy of measurements of 89Sr. The 85Sr impurity present in the 89Sr solution has a significant effect on the response of radionuclide calibrators used in hospitals. A comparison was conducted between the National Physical Laboratory (NPL) and the UK hospital physics community. Only 58% of the results were within 5% of the NPL value. Work at NPL has resulted in correction factors for the NPL secondary standard radionuclide calibrator and for Capintec calibrators, which will produce a significant improvement in performance.