Author’s response

This version was published on 1 November 2008

Ann Clin Biochem 2008;45:618
doi:10.1258/acb.2008.081102
© 2008 Association for Clinical Biochemistry

 

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Letters


While members of the Specialist Advisory Group (SAG) welcome the important work done by Florkowski and colleagues in the development and validation of a diazo method for CSF bilirubin, our confidence in the performance of this method is not yet sufficient for us to feel able to recommend it in the recently revised national guidelines as a screening method (Ann Clin Biochem 2008;45:238–244). A further issue is that the methods used are not validated by the manufacturers for this purpose. In Europe, this would require a CE mark. This is reflected by the crucial point Florkowski et al. make, that each laboratorymust meticulously validate its own analytical performance ofan automated diazo method for CSF bilirubin.

Florkowski et al. admit that further study and quantitation of the negative interference of haemoglobin on CSF bilirubin is required. Moreover, we remain concerned that a discrepancy exists between the net bilirubin absorbance cut-off of 0.007 AU recommended in our guidelines and the absorbance value of 0.015 AU, this value equating to the New Zealand group’s proposed cut-off concentration of 359 nmol/L. We know that patients with SAH may have CSF net bilirubin absorbances of between 0.007 AU and 0.016 AU, and our concern is that such patients may be falsely classified if the diazo method is used.1

It has never been the intention of this group to discouragelaboratories from attempting validation of this methodology,but we are of the view that implementation and introductionof such a method into routine clinical practice represents amajor analytical challenge; namely that of maintaining consistentquality in a user-defined assay employing bilirubin calibrantsand controls at a fraction of the concentrations used for serumassays. Furthermore, were such a ‘rule-out’ assayto be introduced, it would be essential for providers to ensurethat performance of the assay did not delay the spectrophotometricanalysis and interpretive reporting of CSF samples with increasedbilirubin.


Anne M Cruickshank on behalf of the UK NEQAS Specialist Advisory Group for External Quality Assurance of CSF Proteins and Biochemistry


Department of Biochemistry, Southern General Hospital, Glasgow G51 4TF, UK




REFERENCE

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 REFERENCE


  1. Cruickshank A, Auld P, Beetham R, et al. Revised National Guidelines for analysis of cerebrospinal fluid for bilirubin in suspected subarachnoid haemorrhage. Ann Clin Biochem 2008;45:238–44[Abstract/Free Full Text]


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