Hello list members
Having just returned from holiday, I have read with interest the
messages starting with Helen's about testosterone assays and
their internal quality control.
The issue of the availability of internal quality control materials
within the normal female reference range has been a source of
irritation and confusion for many years, and in my capacity as
organiser of the UK NEQAS for this analyte I have often spoken to
instrument manufacturers about this. Some have suggested
diluting with 'zero standard' to achieve a target value between 1.5 &
2.0 nmol/L.
The issue of whether a laboratory should perform an assay without
a suitable control material within the normal range is a professional
and moral one. A purist (like me) would say 'NO'. The assay
should be optimised to cover the required analytical range for the
analyte and controls placed strategically throughout that range and
ideally at the main clinical decision point(s). I believe that
manufacturers of instruments and reagents (and IQC materials)
should face up to this and provide suitable materials.
The problem is that manufacturers see the testosterone assay as a
continuum from 'low' (say 1.0 nmol/L in a fermale) to 'high' (say 50
nmol/L in a male) and provide a number of controls throughout this
range, often without regard to the main (male & female) decision
points. This is scientifically and clinically unsound!
It has long been a hobby horse of mine that testosterone assays
should be separately optimised and controlled for female and male
applications (this is why we separated the UK NEQAS schemes
nearly a decade ago).
Assay systems behave differently: (specificity, recovery,
relationship to GCMS reference values etc) with the different
matrices. Separation of assay systems with improved specificity
and accuracy for the female matrix is urgently required to address
problems of 'true' reference limits, interference with metabolites,
spurious high values (with need for repeat extraction assays) etc.
Analysis of testosterone in the male matrix seems much less
problematical and is performed adequately by most systems.
Perhaps it is time for laboratories to question their suppliers as to
what they are doing to improve optimisation for the female matrix
and/or separate the assays. The tools exist now (eg SysRef
materials) with which accurate comparisons with GCMS target
values can be made and optimisation improved. My guess is that
no manufacture will be able to create an assay that performs well
for both male and female SysRef materials which will further
enforce the need for separate assay systems.
I already anticipate the response - "it is 'too difficult' to implement
and 'market' separate female and male testosterone assay
systems on the one platform" and "customers would have the
additional work load of having to sort out their samples".
I believe that the clinical science of testosterone measurement
should be paramount and drive the necessary technology not the
other way round. What do other list members and manufacturers
think?
JGM
Jonathan Middle PhD
Organiser UK NEQAS for Steroid Hormones
Chairman UK NEQAS Executive
Deputy Director UK NEQAS (Birmingham)
UK NEQAS PO Box 3909 Birmingham B15 3NY
tel 0121 414 7300, fax 0121 414 1179
[log in to unmask] http://www.ukneqas.org.uk
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