Simple and robust ICP-MS method for simultaneous determination of serum Co and Cr in routine clinical practice.

Chromium (Cr) and cobalt (Co) metal ions released from orthopedic prostheses, such as metal-on-metal (MoM) bearings, may be related to wear of the bearing surface. These ions may serve as indicators of the in vivo performance of MoM bearing surfaces. We developed a simple and sensitive assay suitable for the simultaneous measurement of serum Cr and Co using inductively coupled plasma-mass spectrometry (ICP-MS) in clinical routine laboratory practice to evaluate analytical performance and clinical utility. We evaluated the linearity, precision, and lower limit of quantification (LOQ) of an ICP-MS method to determine serum Cr and Co concentration in accordance with U.S. Food and Drug Administration guidance for bioanalytical method validation. This method was used to determine the serum Cr and Co levels of 236 clinical samples from 74 patients with MoM hip prosthesis and 51 healthy controls. The assay showed good linearity (0-20 μg/l, r(2)>0.999) and satisfactory accuracy for all tested concentrations of Cr and Co (%bias, -1.5% to 2.5%, -3.3% to 1.6%, respectively). The CVs for both metal ions were <10% for LOQ (0.02 μg/l Cr, 0.01 μg/l Co) and within 5% for other concentrations (intra- and inter-assay CV, 1.2-2.6 and 1.9-4.4% of Cr; 1.4-2.7 and 1.9-4.7% of Co). The serum Cr and Co concentrations (mean ± SD) were 0.60 ± 0.12 μg/l and 0.29 ± 0.15 μg/l in 51 healthy subjects. In 74 patients (185 serum samples) after HRA (median duration implanted, 48 months; range, 1-138 months), the concentrations of Cr and Co were 2.75 μg/l (range, 0.61-116.80 μg/l) and 1.49 μg/l (range, 0.12-127.80 μg/l), respectively. ICP-MS can simultaneously quantify serum Cr and Co levels with suitable analytical performance including a wide analytical range and very low LOQ. This assay will be very useful for evaluating the nutritional status of Cr and Co in healthy humans as well as monitoring the performance of orthopedic prostheses after hip resurfacing arthroplasty.