Ian said:

"I don’t think that the use of SI units implies anything definite about traceability"

I have always thought and taught to students that you can only use SI units (mole or Kg), (a) if the analyte is JCTLM Type A, and (b) you can trace the result back through a traceability chain to a primary standard containing a known amount of analyte expressed in SI units.

What do the expert metrologists say? Have I been under a misapprehension? (I'm expecting Gunnar Nordin and Anders Kallner to comment!) We must be clear on this if we are to encourage manufacturers to be rigorous in their approach, as if they can use SI units willy-nilly but this doesn't really mean anything, then we are in trouble!

So what should the use of SI units imply in common sense terms?

It must suggest, at the very least, that the manufacturer has acquired a vial of the substance from a reputable source, which has a stated purity and a certificate to prove it, and has made up a standard solution designed to achieve a concentration (with all uncertainties understood and stated), which they use as the starting point in the calibration of their assay. So if the rest of the traceability chain below that standard is unbroken, then the end result will be traceable back to the original material used. The manufacturer should be able to describe this in their technical documentation and reply adequately to user requests for information.

No high order reference material for 3-beta hydroxybutyrate appears to exists, but it can be obtained in pure form from chemical suppliers, so this is where the traceability chain will have to stop. The user of the assay will have to decide whether they accept this in their verification and validation process. If they don't, they will have to get some (better?) pure material of their own and conduct a re-calibration. This will turn the assay into an in-house one, which will require additional hurdles to be surmounted!

Have we opened a can of worms here? It surely must be the manufacturer's responsibility to give assurance to users that their assay is properly calibrated and can meet appropriate analytical and clinical quality specifications! Are they prepared to comment?

Sorry to keep on about this, but it is really important and has widespread implications for laboratories trying to comply with ISO standards and UKAS accreditation requirements.

Cheers

Jonathan

Chair AQMLM

ex IFCC C-TLM member

A couple of references which might be useful
http://link.springer.com/article/10.1007%2Fs00769-010-0640-6
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2556586/

On Thu, Jul 16, 2015 at 12:00 PM, Ian Young <[log in to unmask]> wrote:

It may well be that hydroxybutyrate is a non-standardised measurand and that there is no calibrator or reference material with an international endorsement.

JCTLM doesn’t list a higher order reference material or measurement procedure so far as I can see, and I also can’t see anything obvious in the catalogues of IRMM, NIST or NIBSC.

I don’t think that the use of SI units implies anything definite about traceability.

I do think that Randox should be able to provide additional information about how they assign values in there assay, but it is quite possible that this will not address the need identified by UKAS and that some in-house calibration may be required.

Overall an unsatisfactory situation! I would also be interested in how other manufacturers evidence traceability for hydroxybutyrate.

Best wishes

Ian

IS Young
Professor of Medicine, Queen's University Belfast
Associate Medical Director (Research and Development), Belfast Health and Social Care Trust

Centre for Public Health

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Royal Victoria Hospital
Grosvenor Road
Belfast BT12 6BJ
Northern Ireland

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