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Here's one more vote against the practice of factoring results of a "new" assay to attempt to make them "agree" with the results from the assay being replaced. In addition to the reasons already given by others, I'll add anoher practical consideration. If you introduce a "correction factor" into your chemistry analyzer or computer system, then you must always remember to "unfactor" your results for your proficiency testing samples (I believe they are called external quality assessment samples in the U.K.) before you report these results. Eventually, you will forget to do this and your results will be flagged as "unacceptable". Since proficiency testing is used by regulatory and accreditation agencies in the U.S. (right or wrong) to penalize laboratories who "fail", this is an important consideration on this side of the pond. We implemented the Vitros (then the Ektachem) test for LDH about ten years ago in our laboratory. The results were 2.5 to 3 times those obtained with our old assay (lactate to pyruvate at 30 degrees C). We notified our clinicians of the change in methodology and the new reference interval via our laboratory newsletter and a temporary header on our lab reports. Nevertheless, we still received some phone calls for a short time after the change was implemented and there was the inevitable wailing and gnashing of teeth from the usual suspects (who never read what we send them and then claim they were never notified). But things settled down after a few weeks and I daresay nobody received an adverse clinical intervention for an "elevated" LDH!! The impact of such a change in reference range for LDH should be minor relative to that involved with the switch to SI units. My understanding is that the clinicians in Canada and the U.K. survived this major change admirably! [Hope I haven't started an international incident with this last comment!!] Finally, I must say that I have enjoyed monitoring (and occasionally contributing to) this discussion group over the past 1+ years. The quality of the contributions and the discussion is consistently very high and I particularly enjoy the case discussions prepared by Dr. Challand. Great job! Sal Sena Salvador F. Sena, Ph.D., DABCC Associate Director, Clinical Chemistry and Toxicology Department of Pathology and Laboratory Medicine Danbury Hospital Danbury, CT 06810 Tel 203-797-7705 Fax 203-731-8678 [log in to unmask] %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%