Table 2

Subdivisions according to cobalt (Co) concentrations

Cobalt range (µg/l)
<1Optimally functioning joints. Co concentrations in the range of normal physiological values
1–2‘Normal/expected wear’ and the majority of published studies involving well-functioning hip resurfacing devices report median Co levels in this range31 32
2–5‘Equivocal wear’. The significance of Co concentrations in this range are not currently well understood
5–10‘Increased wear’. A Co concentration ≥5 µg/l is highly sensitive and specific for increased wear of explanted components8
>10‘Excessive wear’. In a healthy individual, Co concentrations >10 µg/l signify unequivocally high rates of wear8