When comparing vancomycin results from an Abbott TDxFLx and an
Abbott AXSYM. we came across marked discrepancies in a patient with
liver disease. He had a very high bilirubin, with most being conjugated
(>300 umol/L). The results in mg/L from the two assays were as folows:
TDX AXSYM
2.6 8.0
15.3 24.1
14.4 20.2
Since then, we have noted lower results by the TDX assay in another
two patients with liver disease and conjugated hyperbilirubinaemia,
although not as marked differences as those above. We have also
obtained plasma from the above patient when he was not receiving
vancomycin plus two other patients with very high conjugated bilirubin
levels and have spiked these plasmas with the drug in concentrations
ranging from 20 to 200 mg/L. Our recoveries of the drug by the AXSYM
assay were close to 100% in most instances but those by the TDX were
considerably lower. Further studies are planned.
We would be interested to know if any other laboratories have deteceted
similar discrepancies or could offer advice about this problem.
Thank you.
John Coakley
Head, Department of Clinical Biochemistry
The New Children's Hospital
Westmead NSW Australia
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