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> Date: Mon, 14 Aug 2000 16:25:34 +0100 > Subject: Controls for Testosterone at levels less than 3.0 nmol/l > From: "Grimes, Helen" <[log in to unmask]> > To: "'ACBUK'" <[log in to unmask]> > Reply-to: "Grimes, Helen" <[log in to unmask]> > We currently use Centaur for male and female testosterone, but lack a > normal/low female testosterone control level. The ligand controls supplied > by Bayer only go as low as 3.6 nmol/l. We changed from DPC CAC testosterone > to Centaur, and note an increase in the number of female elevated > testosterone, i.e around 3.8-4.0 nmol/l, so either we missed females before, > or have the wrong reference range (0.2-3.0) or we have interfering > substances. Theorists will say we should confirm with extraction methods, > but who is doing that nowadays? We know our CVS at the low end are about > 15%, and so feel a lower control would be helpful. Has anyone located such a > control? > I agree with Mike Diver in that methods for female testosterone do not appear to have progressed much over the last 20 or so years. We recently transferred our testosterone assay to an automated analyser (Abbott Architect) but still use our extraction method on all high female samples (>3.0 nmol/l). Many repeat quite well but there are a relatively large number of samples where the extraction method gives substantially lower results bring what would have been a worryingly high testosterone result back into the reference range. I do not think the solution is to increase the reference range for the direct assay as you may then miss truly high results. This problem occurs to a greater or lesser extent with all direct testosterone methods and there has been much debate over the years on its cause. As there only appear to be large discrepancies with some samples I think that it must be due to interfering substances (probably steroid conjugates). To get a lower QC pool we have diluted as Mike suggests with hormone free serum or you could try horse serum which contains low levels of testosterone. Mr. John Kane Clinical Biochemistry Dept Hope Hospital Salford M6 8HD Tel. 0161 787 4374 Fax. 0161 788 7443 Email [log in to unmask] %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%