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Metal on Metal Metal Ion Analysis in Patients with Metal-on-Metal Hip Replacements: Whole Blood vs. Serum

Josephine

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Metal Ion Analysis in Patients with Metal-on-Metal Hip Replacements: Whole Blood vs. Serum
PAPER NO. 309
Karren M. Takamura, BA, Los Angeles, CA
Antoni Nargol, FRCS, Yarm, United Kingdom
Andrew Taylor, MD, Surrey, United Kingdom
David Langton, Gateshead, United Kingdom


INTRODUCTION: Currently, there is no consensus as to whether serum, whole blood and/or red blood cell fraction should be used to monitor the performance of the bearings. Therefore, it is important to determine the appropriate sample collection protocol to assess implant wear. This study’s aim was to determine the distribution of chromium and cobalt in blood fractions.

METHODS: The distribution of metal ions in the whole blood and serum fractions: Whole blood Cr and Co samples were compared to the corresponding serum Cr and Co samples in patients with unilateral hip resurfacings. Univariate linear regression was used to examine the relationship between matched blood Cr and serum Cr samples. In vitro study of chromium species distribution in human blood:

Blood was collected from a healthy adult volunteer into (i) a container with EDTA as anticoagulant and (ii) a plain container. The anti-coagulated blood was divided into a series of portions and each was spiked with solutions of Cr3+ or Cr6+ so as to increase the concentration by 0, 2, 5, 10 or 40µg/L. These samples were further divided into four aliquots, which were separated into plasma and washed red blood cells (RBCs) after 45 min, four, 24 and 48 hours at room temperature. The non anti-coagulated blood was immediately divided into portions, similarly spiked with Cr3+ or Cr6+, allowed to clot and the serum separated. The concentrations of Cr were measured in RBCs and serum by ICPMS.

RESULTS: The distribution of metal ions in whole blood and serum fractions: A total of 450 blood samples were sent for whole blood and serum metal ion analysis. There was a highly significant correlation between increasing whole blood Cr concentrations and an increasing serum Cr to blood Cr ratio (r = -0.485, p < 0.001). Serum Co correlated well with blood Co (r = 0.953 p < 0.001) and the concentrations of Co in the two fractions showed less variability than the Cr samples. Results of in vitro study: Blood samples spiked with Cr3+ showed preferential increase in Cr concentrations in the serum fractions. This was in contrast to blood samples spiked with Cr6+, where there was a preferential increase in Cr in the RBCs. The time from sampling to removal of plasma cells had a very small effect on overall measured Cr concentrations and the distribution of the Cr species between the RBCs and plasma/serum.

DISCUSSION AND CONCLUSION: The results suggest that as wear increases, metal ions are taken preferentially into the serum fraction of blood. It has been shown that Cr6+ ions generated from corrosion processes are preferentially taken into red blood cells, a result which was replicated in the current study. Cr3+ is believed to have a greater affinity for serum proteins and is thought to be the predominant Cr species produced by mechanical wear. This leads us to speculate that the increase of serum Cr concentrations to levels greater than those found in whole blood is secondary to an increased rate of wear rather than corrosion processes.
 

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