Evaluation of the Method for Analyzing Chromium, Cobalt and Titanium Ion Levels in the Blood Following Hip Replacement with a Metal-on-Metal Prosthesis

High-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) can be used to measure metal ion levels in whole blood, although the accuracy and repeatability of this method is not yet known in the clinical setting. In this study, chromium, cobalt and titanium ion levels were measured in three whole blood samples, each collected at the same moment from 101 patients undergoing total hip arthroplasty with a metal-on-metal (MoM) bearing. The first sample (purge sample) had direct contact with the metal needle used during insertion of the catheter, whereas the second sample (reference sample) and the third sample (reserve sample) did not. The absolute difference between reference samples and reserve samples was greater than the limit of quantification of the HR-ICP-MS device for all three ions (0.84 versus 0.35 g/L for chromium, 0.74 versus 0.07 for cobalt, and 0.88 versus 0.70 g/L for titanium), although the levels were very small in most cases, they exceeded the clinical significant threshold in 19 to 31 of the cases. No clinically significant difference was observed between reference samples and purge samples. Therefore, HR-ICP-MS is a clinically acceptable method to evaluate metal ion levels in blood following hip replacement with an MoM prosthesis, and it is not necessary to discard the purge sample to obtain repeatable results.