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Dear Colleagues Our laboratory has been involved in a prospective study (so far over 7 years) on a large group of patients and measuring their cardiovascular disease risk factors. One of these factors is homocysteine. For the first three surveys we measured homocysteine by HPLC - (very expensive and tedious). For the more recent survey homocysteine was assayed on the Abbott AxSym method using samples that had been frozen at -20C for approximately 6 months. When we initially compared the HPLC results with those from the AxSym the slope was 1.005, intercept was 0.21 and r2 was 0.997, using fresh samples. We have repeated this analysis on the stored samples and obtained a slope of 0.955, an intercept of 1.65 and r2 of 0.273. I am concerned about the loss of correlation between the two methods on the stored samples. Does anyone have information on the performance of the AxSym on stored samples or can suggest a reason for this change? Regards John Dr John Beilby Senior Biochemist Clinical Biochemistry PathCentre Locked Bag 2009 Nedlands Western Australia 6009 Tel 61 8 9346 2368 Fax: 61 8 9346 3882 [log in to unmask] ------ACB discussion List Information-------- This is an open discussion list for the academic and clinical 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. ACB Web Site http://www.acb.org.uk List Archives http://www.jiscmail.ac.uk/lists/ACB-CLIN-CHEM-GEN.html List Instructions (How to leave etc.) http://www.jiscmail.ac.uk/