Sunday, October 16, 2011

Sensitivity and specificity of blood cobalt and chromium metal ions for predicting failure of metal-on-metal hip replacement.


Interesting study.  This is the first one I have seen that examines the predictive nature of blood ion levels for diagnosing hip failure.  They seemed to find the optimal cut off level for the Cr Co blood tests were about 5ppb or 5 mcg/l.   (Likely that you have received your metal tests in micrograms per liter which is I believe the same as parts per billion (PPB )]

Thier conclusion was that Blood metal ions had good discriminant ability to separate failed from well-functioning hip replacements.

So If I look at my test results, they are way over the cut off:


Chromium Blood ion test taken on 1/4/11
Cobalt blood ion test taken on 1/4/11
24 hour Urine chromium test taken on 1/30/11
Other Urine chromium test taken on 1/30/11
Cobalt Urine test taken on 1/30/11
2nd blood chromium test taken on 2/9
2nd blood cobalt test taken on 2/9
Actual result
28mcg/l
34 mcg/l
86
49
> 10.0 ug/l
21.6 ug/l
29.5 ug/l
Reported normal level
<2mcg/l
<1.8mcg/l
.6
.5
.1-.2
.5 ug/l
<1ug/l
Multiple over normal
14x
18.8x
143x
98x
5-100 x
43.2x
30x

J Bone Joint Surg Br. 2011 Oct;93(10):1308-13.

Source

Imperial College London, Department of Musculoskeletal Surgery, Charing Cross Hospital Campus, Fulham Palace Road, London W6 8RF, UK.

Abstract

Blood metal ions have been widely used to investigate metal-on-metal hip replacements, but their ability to discriminate between well-functioning and failed hips is not known. The Medicines and Healthcare products Regulatory Agency (MHRA) has suggested a cut-off level of 7 parts per billion (ppb). We performed a pair-matched, case-control study to investigate the sensitivity and specificity of blood metal ion levels for diagnosing failure in 176 patients with a unilateral metal-on-metal hip replacement. We recruited 88 cases with a pre-revision, unexplained failed hip and an equal number of matching controls with a well-functioning hip. We investigated the 7 ppb cut-off level for the maximum of cobalt or chromium and determined optimal mathematical cut-off levels from receiver-operating characteristic curves. The 7 ppb cut-off level for the maximum of cobalt or chromium had a specificity of 89% and sensitivity 52% for detecting a pre-operative unexplained failed metal on metal hip replacement. The optimal cut-off level for the maximum of cobalt or chromium was 4.97 ppb and had sensitivity 63% and specificity 86%. Blood metal ions had good discriminant ability to separate failed from well-functioning hip replacements. The MHRA cut-off level of 7 ppb provides a specific test but has poor sensitivity.

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