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Dear Johathan: I suppose it's fair to say that just about any ingested amount of ethylene glycol or methanol is clinically significant, but I have always been told that a concentration of at least 20 mg/dL (apologies for the archaic American units) will prompt clinical intervention. At that concentration, methanol only raises the osmol gap about 6 mOsm, and ethylene glycol half that. Taking into account the error in osmolality measured by most freezing point osmometers, it is very possible to have a clinically significant intoxication without an elevated osmolar gap. Given the toxicity of these volatiles, our clinical toxicology staff would initiate agressive treatment based on suspicion alone, even if the osmolar gap was normal. I haven't heard of any lab that could measure methanol or ethylene glycol fast enough to postpone treatment for the lab result, and I'm not sure the analytical method exists that can rise to that challenge. GC would take a couple of hours, minimum. It would be useful to be able to discharge a patient sooner if the test came back negative, but none of the clinical laboratories in Jacksonville performs these tests on a STAT basis. I considered setting it up several years ago, but the GC methods for methanol and ethylene glycol are different--EG requires derivatization--so it was simply impractical. We measure ethanol on an automated chemistry analyzer using an alcohol dehydrogenase method, and the turnaround time is no longer than it would be to report an osmol gap--about 45 minutes once we receive the specimen. Roger Roger L. Bertholf, Ph.D. Associate Professor of Pathology Director of Clinical Chemistry & Toxicology University of Florida Health Science Center/Jacksonville -----Original Message----- From: Jonathan Kay [mailto:[log in to unmask]] Sent: Thursday, June 05, 2003 5:53 PM To: [log in to unmask] Cc: Jonathan Kay; Roger Bertholf; David Brown Subject: Rapid detection of alcohol, was Re: 'Screening' test for alcohol Osmolality (calc) = 2 x Na + Glucose + urea (all measurements in mmol/L) seems to work clinically or http://www.google.com/search?q=osmolar+gap&ie=UTF-8&oe=UTF-8 I think the clinical need for is a quick method to "suggest" accumulated unusual solute, so that it is possible to rapidly identify which patients need further investigation and which don't. http://www.sydpath.stvincents.com.au/tests/Osmolality.htm says: "The normal osmolar gap is up to 10 mmol/L and values in excess of this usually indicate the presence of an exogenous agent. The most common by far is ethanol, but methanol, ethylene glycol, acetone and isopropyl alcohol can occasionally be present in sufficient quantities to produce an increased osmolar gap. Importantly significant toxicities, particularly from ethylene glycol, can occur with a normal osmolar gap as the toxic concentrations are quite low. With the passing of time from ingestion of these substances the osmolar gap falls as the anion gap rises due to conversion to negatively charged substances." I was surprised by this suggestion of inadequate sensitivity, but it is consistent with Roger Bertholf's earlier posting. Does anyone have more information on whether we might be missing patients we ought to be treating? I'd be interested to know from laboratories which use a more specific analytical approach how quickly you get the required information in practice. Jonathan On Thursday, Jun 5, 2003, at 21:51 Europe/London, David Brown wrote: Can someone put me straight on the formula for measuring/calculating osmolar gap? Is it the difference between the "calculated" and measured osmolality? Is there now a reference/standard for calculating osmolality? It think it might be OK to "suggest" the probability of an alcohol ingestion in the light of a significant "osmolar gap", but............. David Brown --- Jonathan Kay <[log in to unmask]> wrote: Seems to work OK for us. In practice clinicians request "ethanol" and we measure the osmolar gap... they don't request "osmolar gap". We refer requests for individual alcohols to a toxicology unit. Occasionally we have to remind clinicians that it may be necessary to treat before the results of assaying individual alcohols are available A and E handbooks should have guidance on ethanol, methanol and ethylene glycol poisoining, written in collaboration with the lab... I think it is important the timing aspects are in the protocol. Methanol poisoning is very rare in the UK compared to the USA... Was this point covered in the Annals review of toxicology requirements? Jonathan On Thursday, Jun 5, 2003, at 10:30 Europe/London, Borland, Bill wrote: I would be interested to hear any views on the use of the Osmolal Gap as a screening test for Ethanol. (Coakley at al, Pathology, 1983,15, 321) One of the A&E departments within our Trust uses the Osmolal Gap as a 'screening' test for alcohol and in only a few clinical situations do they require a more specific assay for ethanol. They have used the Gap in this way for many years and I suspect were encouraged to do this by the lab in the days when it was easier to measure serum osmolality than ethanol, especially out of hours. The danger is that junior medical staff may not be aware of the limitations of this approach and delay identification of a possible methanol or ethylene glycol poisoning. Should we be discouraging them? It would be useful to find out the practice in other centres. William Borland Principal Biochemist (Toxicology) Biochemistry Department North Glasgow NHS Trust Gartnavel General Hospital Glasgow G12 0YN Tel 0141 211 3343 Fax 0141 211 3452 Email bill.borland.wg@northglasgow .scot.nhs.uk _________________________________________________________________ The information contained within this e-mail and in any attachments is confidential and may be privileged. If you are not the intended recipient, please destroy this message, delete any copies held on your systems and notify the sender immediately. You should not retain, copy or use this e-mail for any purpose, nor disclose all or any part of its content to any other person. 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