It seems therefore that there are very few absolutes. As most things are
relative and poorly understood perhaps we need some degree of pragmatism and
incomplete models to make progress. If the model is simple and works most of
the time use it and accept these imperfections. Everything is as work in
progress. You get 80% of the benefit for 20% of the work.
Hope your inspection goes well.
mike


-----Original Message-----
From: Clinical biochemistry discussion list
[mailto:[log in to unmask]] On Behalf Of Jonathan G. Middle
Sent: 23 November 2006 13:51
To: [log in to unmask]
Subject: FW: Quantities and properties

 
Taking a break from preparing for our CPA EQA inspection!!


Definitions of 'analyte' on the web
===================================

# the substance which a laboratory test aims to detect. In cholesterol
testing, for example, the analyte is cholesterol. In genetic testing, the
analyte could be, for example, a specific allele or genetic mutation.
www.cs.uu.nl/people/ronnie/local/genome/a.html

# (an·a·lyte) (an¢[schwa]-l[imacr]t) a substance undergoing analysis.
www.mercksource.com/pp/us/cns/cns_hl_dorlands.jspzQzpgzEzzSzppdocszSzuszSzco
mmonzSzdorlandszSzdorlandzSzdmd_a_34zPzhtm

# A substance measured in the laboratory. A chemical for which a sample
(such as water, air, or blood) is tested in a laboratory. For example, if
the analyte is mercury, the laboratory test will determine the amount of
mercury in the sample (ATSDR 2003).
www.racteam.com/LANLRisk/Glossary.htm

# Identifies the analyte that was measured. See Analyte Categories With
Associated Analytes for association between analyte category and analyte.
www.cropcomposition.org/databaseorg/Glossary%20of%20Terms.htm

# The substance measured by a laboratory test; for instance, a specific
mutation or allele.
www.cdc.gov/genomics/gtesting/ACCE/FBR/CF/CFGlossary2.htm

# Substance to be measured.
ojjdp.ncjrs.org/PUBS/drugid/glossary.html

# A name given to describe a substance which is being produced in an
analytical procedure.
www.pestmanagement.co.uk/lib/glossary/glossary_a.shtml

# A chemical being tested for in a laboratory test.
www.rrmsc.com/resources/glossary.htm

# An Analyte is the substance or chemical constituent that is undergoing
analysis. The substance being measured in an analytical procedure.
en.wikipedia.org/wiki/Analyte

======================

The common theme seems to be 'a substance that is measured/analysed in a
laboratory'.  
I fear we may get into more arguments if we come to define 'substance',
'measure' or 'laboratory!

I can't make any statements about the physical world because this may just
be a construct of my consciousness, which may itself just be an emergent
property of brain complexity!

======================

To be constructive though, is this all about naming things?  We use the
scientific process to refine our knowledge of the components of the natural
world and in clinical biochemistry we concentrate on the components of
biological systems, especially those that help us understand health and
disease.  We observe, separate out, analyse, purify, characterise things and
give them names.  By doing so we actually bring those things into existence
in our 'universe of discourse' so that we can refine techniques to study
them and ultimately measure them for the good of patients.  Some things are
physical entities which we can separate out and name and others are
attributes (I hesitate to call them properties!) because we don’t know
enough about what generates what we observe.

Some things are easy to name and are truly unique - elements, simple
compounds etc.  Others are more difficult - proteins etc - which are
heterogeneous and exist in multiple forms in health and disease.  In respect
of the latter we end up with names of things that imply uniqueness (to us
and our customers) but the reality is different.  JCTLM classify 'analytes'
as type 1 (the easy ones as above) and type 2 (the difficult ill-defined
ones)  

The ordinary man in the street would naturally assume that if we say we are
measuring analyte X in his blood, then analyte X must exist and we must know
exactly what analyte X is otherwise we can't possibly measure it.  I try to
understand what Roger and Anders are saying but I could not possibly explain
their detailed metrological philosophy to a patient (or a doctor).
Enjoyable as this discussion has been we cannot escape the fact that we have
to agree amongst ourselves what we do and then communicate this to a lay
public.  So in Mike's real world of 'consensus reality' where we have to
demonstrate and prove to our customers and paymasters that what we do adds
value to the clinical event, we must be sure in our own minds what we mean
by these words.  

As a starting point for discussion, might we agree on the following working
‘common sense’ concepts for the 'things' that we list in our test
repertoire:

Type 1 component - an entity which is uniquely named, chemically defined,
exists in the same form wherever it is encountered, where a standard exists
which can calibrate measurement procedures, and where results can be
expressed in method-independent SI units of mass or molar amount - eg
Cortisol

Type 2 component - a group of closely related entities which share structure
and function and thus may be named under a single heading, which can be
purified and characterised to some extent, but without certain knowledge
that these entities are the same in the standard material as are in the
patient, and where results are expressed in arbitrary units which are
method-dependent - eg TSH

Attribute - an observed characteristic of a sample which can be quantitated
in arbitrary unitage in a defined system - eg ‘ischaemia modified albumin’
(serum cobalt binding)

These are all analytes (probably) but we have to think about them in
different ways when we discuss and assess comparability, trueness,
uncertainty, standardisation and traceability and when we communicate to our
users on their meaning and significance.

My assertions:

Type 1 component - absolutely no option but to achieve common
standardisation and harmonised results using established reference
measurement systems with true metrological traceability

Type 2 component - the way forward for many of these is exemplified in the
approach taken by the the ISOBM TD-7 Workshop on hCG and related molecules :
Berger et al. Towards user-oriented standardization of pregnancy and tumor
diagnosis: assignment of epitopes to the three-dimensional structure of
diagnostically and commercially relevant monoclonal antibodies directed
against human chorionic gonadotropin and derivatives. Tumour Biol. 2002
Jan-Feb;23(1):1-38.

Attribute - more hard scientific work to sort out what is going on before we
make claims about what is being measured and how useful it is.    

Sorry if this is repeating myself and maybe stating the obvious!

Hope this is helpful

J

Back to the Quality Management System now!


Dr Jonathan Middle
Deputy Director, UK NEQAS Birmingham
0121 414 7300, fax 0121 414 1179
-----------------------------------------------
All opinions expressed in this email are mine alone and are not necessarily
representative of the views of the UK NEQAS organisation, UK NEQAS
Birmingham (Wolfson EQA Laboratory), University Hospital Birmingham NHS
Foundation Trust or University of Birmingham.



-----Original Message-----
From: Clinical biochemistry discussion list on behalf of Mike Toop
Sent: Wed 22/11/2006 19:58
To: [log in to unmask]
Subject: Re: Quantities and properties
 
Pedantry is a great spectator sport!

Here is my (brief ) 5 pence worth

What do we mean by analyte and how does that definition relate to the
physical world?

 

Mike 

 

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------ACB discussion List Information--------
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community working in clinical biochemistry.
Please note, archived messages are public and can be viewed
via the internet. Views expressed are those of the individual and
they are responsible for all message content.
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