This posting raises several important issues, about which I could rant for England. I will spare you all that of course, but here are some observations:
The classical text book values are not correct. The methods used in those days were up to 30% positively biased from reference method values.
The present Centaur method is positively biased at low concentrations of cortisol and negatively biased at high concentrations to IDMS reference values. In my most recent IDMS-targeted pool exercise, the slope of the regression line for Bayer Centaur was less than 80% but the intercept was significant at about 54 nmol/L. The method that was absolutely spot on was the Bayer Immuno 1 method - now disappearing from use.
Penny Clark's papers are the ones to read about this - she and colleagues have done some interesting work on Synacthen test values from different methods. Just put "clark p cortisol" into PubMed at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed and try reference number 8 as a starting point.
If you participate in my EQA service, you can find the cortisol GCMS exercise as a pdf under the 'scheme' button on our results and reports website.
Hope this helps
Dr Jonathan Middle
Deputy Director, UK NEQAS Birmingham
0121 414 7300, fax 0121 414 1179
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-----Original Message-----
From: Clinical biochemistry discussion list on behalf of Patel Bharat (RWG) West Hertfordshire TR
Sent: Wed 16/11/2005 14:29
To: [log in to unmask]
Subject: Synacthen test
Dear Mail base,
We have been having problems with interpreting cortisol response to
synacthen. What should the cortisol result be for the different time
intervals.
We use the Centaur analyser and compared our cortisol results against
another analyser and the two results were different.
So in light of the cortisol results we changed the cortisol responses(with
the endocrine team):
Before we were using >200 nmol/L as the difference between 0 and 30' and the
30' as >550 nmol/L. This is what's in standard endocrine books and was
educated as being adequate response.
Now we use >100 nmol/l as the difference between 0' and 30' and the 30' at
450 nmol/L and gone away with the 60' sample.
What do other labs use as their cut-offs? Is it published?
Thank you and I'll collate all the responses.
Bharat Patel
Consultant Biochemist
Watford General Hospital
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