Blood metal ion analysis
Whole blood was drawn from a vein in the forearm using an intravenous catheter (venesection) in our hospital (Becton Dickinson Venflon Pro™, 1.5 × 45 mm, Helsingborg, Sweden). After venipuncture, the steel needle was removed, and the blood (5–10 ml) was allowed to flow directly into a 15 ml metal free polypropylene tube (VWR International, CS500, Radnor, PA, US). The blood was stored at minus 20°C until further handling. The concentration of chromium, cobalt, nickel and zirconium in whole blood was determined by Inductively Coupled Plasma–Mass Spectrometry (ICP‐MS). The instrument (Element XR™ HR‐ICP‐MS, Thermo Fisher Scientific, Bremen, Germany) was equipped with a high resolution, magnetic sector field. Before analysis, an aliquot of approximately 1.5 g whole blood was acid digested by adding 3 ml 60% ultrapure HNO