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Dear Colleagues, I am trying to see if anyone (especially in Australia!) is having similar problems to ourselves with low level TSH measurements on the Immulite (original model). There seem to be two possibly unrelated problems. Several months ago we noted an increase in the values of the results determined at the low end of the assay. The number of samples we had with results below the functional sensitivity (0.01 mIU/L) fell markedly compared to previously. Samples from many patients with clear elevations of free T4 and free T3 gave detectable TSH up to 0.1 mIU/L. Testing of these samples on an AxSYM analyser gave undetectable TSH results. We have seen no change in our internal QC or external QA but there are not many samples down at these levels. This has occurred with lot numbers 293, 295, 296 and 297. The apparently false positive TSH results mentioned in the paragraph above generally give the same positive result when repeated or after serial dilution (when multiplied by the dilution factor). However a subset of samples with clearly positive results give a zero reading after a 1/2 dilution in buffer or TSH-free serum. For example a result of 0.1 becomes <0.01 after a 1/2 dilution. We are completely uncertain as to the cause, or the relationship of this phenomenon to the apparent upwards shift. We have changed to a new tube types (BD SSTII and PSTII, not sure if these are in the UK yet) but the timing does not fit exactly with the discovery of the issue. We are in active discussion about this with DPC. Any thoughts welcome. Graham Dr Graham Jones Staff Specialist in Chemical Pathology St Vincent's Hospital, Sydney Ph: (02) 8382-9160 Fax: (02) 8382-2489 ********************************************************************** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This footnote also confirms that this email message has been virus scanned and although no viruses were detected by the system, St Vincent's Hospital accepts no liability for any consequential damage resulting from email containing any computer viruses. ********************************************************************** ------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/