hello
I am not conversant with clinical practice in this area or on the use
of Troponin measurements in the diagnosis and management of MI,
but I have grave concerns where people may 'treat by number' when
important clinical decision points lie at analyte concentrations
where the uncertainty of measurements is high.
What is the imprecision of a typical laboratory's (not a
manufacturer's formal evaluation report) Troponin T measurement
procedure at 0.01, 0.02, 0.05, 0.1 ug/L?
Taking the cut-off point of acceptable imprecision as 10%, 15%, or
20% what then would be the lower limits of the working range of
such a procedure?
What is the within-patient variability of repeat measurements at
these levels (if this concept is valid in a dynamic situation)?
What is the overall between-laboratory agreement of Troponin T
'measurements' at these levels using the same or different
procedures?
In direct terms, taking all these uncertainty factors into account, if
you have a cut off of "0.05 ug/L", what would be the 95%
confidence interval of the range of values that might be obtained by
all laboratories that would include "0.05ug/L"? (Repeat for the
other cut-off limits suggested.)
Do the answers to these questions suggest that the cut-off limits
indicated in these postings are useful in defining and harmonising
best practice on a regional / national / international basis?
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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