title: Evidence against implant-derived cobalt toxicity: case report and retrospective study of serum cobalt concentrations in an orthopedic implant population.
abstract: OBJECTIVE
  Cobalt (Co) exposure has been documented to result in increased erythropoiesis. To evaluate the potential for implant-derived Co toxicity, we examined the relationship between serum Co (sCo) and erythrocyte counts (ERY) in a metal-containing total-hip arthroplasty implant population.
  
  
  METHODS
  Retrospective review of sCo concentrations identified 77 patients with concomitant ERY. Statistical analysis was performed to determine if there was a significant difference in ERY for patients divided into clinically relevant sCo ranges. A single detailed case review of a patient with a loose mal-positioned acetabular component and significantly elevated sCo was also performed for symptoms thought to arise from Co toxicity.
  
  
  RESULTS
  Statistical difference in ERY was not observed between patients with significantly elevated (>10 ng/mL), elevated (4-10 ng/mL), modestly elevated (1.0-3.9 ng/mL), or normal (<1.0 ng/mL) sCo. While the detailed case report was unremarkable for any of the clinical symptoms previously reported to be associated with Co toxicity and no increase in ERY was observed, this patient's sCo was 84 ng/mL.
  
  
  CONCLUSIONS
  Increased erythropoiesis was not observed in patients with implant-derived increased sCo. Even with a sCo 100 × the upper-limit of normal, the patient presented did not have increased ERY nor exhibit any symptoms ascribed with Co toxicity.
authors.affiliation: Department of Laboratory Medicine & Pathology, Mayo Clinic, Rochester, MN, USA. Electronic address: ntolan@bidmc.harvard.edu.
authors.forename: Nicole V
authors.initials: NV
authors.lastname: Tolan
authors.affiliation: Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN, USA.
authors.forename: Rafael J
authors.initials: RJ
authors.lastname: Sierra
authors.affiliation: Department of Laboratory Medicine & Pathology, Mayo Clinic, Rochester, MN, USA.
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Moyer
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging; D000328:Adult; D000368:Aged; D003035:Cobalt / Q000009:adverse effects* / Q000097:blood*; D004906:Erythrocyte Count; D005260:Female; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010388:Pelvis / Q000000981:diagnostic imaging; D011859:Radiography; D012189:Retrospective Studies
chemical_list: D003035:Cobalt
keywords: Cobalt toxicity; Erythropoiesis; Orthopedic implant; Total hip arthroplasty