Table III.
Sensitivity and specificity of whole blood cobalt (Co) and chromium (Cr) for identifying abnormal wear defined as a wear rate ≥ 2 mm3 per year. The area-under-curve (AUC) value for Co was 0.971 (95% confidence interval (CI) 0.965 to 0.977) and 0.959 (95% CI 0.935 to 0.982) for Cr. The most clinically useful values after consideration of sensitivity and specificity are bolded (PPV, positive predictive value; NPV, negative predictive value)
| Whole blood (µg/l) | Sensitivity (95% CI) | Specificity (95% CI) | PPV | NPV |
|---|---|---|---|---|
| COBALT | ||||
| 1.900 | 0.973 (0.898 to 0.998) | 0.667 (0.435 to 0.837) | 0.922 | 0.857 |
| 2.290 | 0.959 (0.880 to 0.990) | 0.667 (0.435 to 0.837) | 0.921 | 0.800 |
| 2.420 | 0.959 (0.880 to 0.990) | 0.722 (0.487 to 0.876) | 0.933 | 0.813 |
| 2.470 | 0.959 (0.880 to 0.990) | 0.778 (0.541 to 0.913) | 0.946 | 0.824 |
| 2.500 | 0.945 (0.862 to 0.982) | 0.833 (0.598 to 0.948) | 0.958 | 0.789 |
| 2.800 | 0.945 (0.862 to 0.982) | 0.889 (0.657 to 0.979) | 0.972 | 0.800 |
| 3.210 | 0.932 (0.845 to 0.973) | 0.889 (0.657 to 0.979) | 0.971 | 0.762 |
| 3.260 | 0.918 (0.828 to 0.964) | 0.889 (0.657 to 0.979) | 0.971 | 0.727 |
| 3.540 | 0.904 (0.811 to 0.955) | 0.889 (0.657 to 0.979) | 0.971 | 0.696 |
| 4.500 | 0.904 (0.811 to 0.955) | 0.944 (0.720 to 1.000) | 0.985 | 0.708 |
| 4.700 | 0.890 (0.795 to 0.945) | 0.944 (0.720 to 1.000) | 0.985 | 0.680 |
| CHROMIUM | ||||
| 5.720 | 0.945 (0.862 to 0.982) | 0.722 (0.487 to 0.876) | 0.932 | 0.765 |
| 5.800 | 0.945 (0.862 to 0.982) | 0.778 (0.541 to 0.913) | 0.945 | 0.778 |
| 6.000 | 0.945 (0.862 to 0.982) | 0.833 (0.598 to 0.948) | 0.958 | 0.789 |
| 6.280 | 0.932 (0.845 to 0.973) | 0.833 (0.598 to 0.948) | 0.958 | 0.750 |
| 6.860 | 0.932 (0.845 to 0.973) | 0.889 (0.657 to 0.979) | 0.971 | 0.762 |
| 6.920 | 0.918 (0.828 to 0.964) | 0.889 (0.657 to 0.979) | 0.971 | 0.727 |
| 7.180 | 0.904 (0.811 to 0.955) | 0.889 (0.657 to 0.979) | 0.971 | 0.696 |
| 7.220 | 0.890 (0.795 to 0.945) | 0.889 (0.657 to 0.979) | 0.970 | 0.667 |
| 7.630 | 0.877 (0.779 to 0.935) | 0.889 (0.657 to 0.979) | 0.970 | 0.640 |
| 7.850 | 0.863 (0.763 to 0.925) | 0.944 (0.720 to 1.000) | 0.984 | 0.630 |
| 8.250 | 0.849 (0.747 to 0.915) | 0.944 (0.720 to 1.000) | 0.984 | 0.607 |
| 8.370 | 0.849 (0.747 to 0.915) | 1.000 (0.789 to 1.000) | 1.000 | 0.621 |
| 8.420 | 0.836 (0.732 to 0.904) | 1.000 (0.789 to 1.000) | 1.000 | 0.600 |