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Colleagues, I agree that predicting the sodium after rehydration and glucose lowering with the formula: expected change in sodium = glucose / 4 (all in mmol/L) is simple and in my experience works remarkably well (any references?). Of course it is not all physiology as the treating doctors can adjust their fluids to assist with this. In response to the question of adding glucose to a solution and its effect on sodium measurement (thanks Trevor), we did find a small effect of very high glucose on direct ISE measurements some time ago. Glucose interference in direct ion-sensitive electrode sodium measurements Asila Al-Musheifri and Graham R D Jones Abstract Circulating sodium concentration is commonly measured by both direct and indirect ion-sensitive electrode (ISE). We describe an unusual case with a high elevation of serum glucose (162 mmol/L) where direct ISE sodium measurement was 9 mmol/L higher than the indirect measurement in the absence of any cause for pseudohyponatraemia. In vitro experiments showed that very high glucose concentrations increased the sodium in direct, but not in indirect ISE measurement. This effect was insufficient to account for the entire difference between the measurements seen in the patient, indicating that other factors, for example pH and bicarbonate concentration, must also be involved. This effect may influence interpretation of sodium status in patients with gross hyperglycaemia. Ann Clin Biochem 2008; 45: 530-532. Regards, Graham Graham Jones Staff Specialist in Chemical Pathology St Vincent's Hospital, Sydney (02) 8382-9160 www.sydpath.com.au From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of Bertholf, Roger Sent: Tuesday, 14 October 2014 9:03 AM To: [log in to unmask]<mailto:[log in to unmask]> Subject: Re: Corrected sodium in DKA Hyperproteinemic and hyperlipidemic pseudohyponatremia are volume exclusional phenomena; sodium (and other electrolytes) is excluded from the non-aqueous volume. Direct potentiometry is not affected because it is a volume-independent measurement. Indirect potentiometry is affected because it is volume dependent, since a specimen dilution is required. Hyperglycemic (or hyperosmotic) pseudohyponatremia does not affect either direct or indirect potentiometric measurements. It is a dilutional phenomenon since hyperosmotic blood, due to high glucose, draws water from tissues into the vasculature, diluting all constituents. The only thing the two phenomena share is a name. Roger Roger L. Bertholf, PhD Professor of Pathology and Laboratory Medicine University of Florida College of Medicine From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of Trevor Walmsley Sent: Monday, October 13, 2014 4:34 PM To: [log in to unmask]<mailto:[log in to unmask]> Subject: Re: Corrected sodium in DKA Food for thought - if you added glucose to a solution containing sodium ions would this change the activity of the sodiums ions - if the answer is no then a direct sodium measurement from a blood gas analyser should not be corrected. Would anyone care to enlighten as I don't know the answer? cheers Trevor "A normal person is one that has not been fully investigated" Trevor Walmsley Senior Scientific Officer Canterbury Health Labs Christchurch New Zealand Phone: +64 3 364 0317 Mobile: 027 423 5135 Fax:Phone: (0064 3) 364 0320 eMail: [log in to unmask]<mailto:[log in to unmask]> https://www.researchgate.net/profile/Trevor_Walmsley?ev=hdr_xprf$$ ________________________________ From: Clinical biochemistry discussion list [[log in to unmask]] on behalf of Tuddenham Emma (CROYDON HEALTH SERVICES NHS TRUST) [[log in to unmask]] Sent: 14 October 2014 01:20 AM To: [log in to unmask]<mailto:[log in to unmask]> Subject: Corrected sodium in DKA Dear all We have had a query from one of our paediatricians re. whether we would recommend correcting sodiums for raised glucoses in patients with DKA. This is mentioned in the recent BSPED guidelines: http://www.bsped.org.uk/clinical/docs/DKAGuideline.pdf The formula they are advocating is: Corrected Na = Measured Na + 0.4(glucose - 5.5) I believe the argument for correcting for the dilutional effect of glucose is that you may get a better idea of the 'true' sodium and can follow this during fluid resuscitation. If it fails to rise on treatment as the glucose falls then you may have increased risk of cerebral oedema. I cannot find much evidence for this formula in the literature - is anyone advocating a similar approach? I don't think we would want to report this in the lab (even assuming we had a lab glucose available), but the paediatrician is quite keen to use it as a rule of thumb. Many thanks, Emma Emma Tuddenham Clinical Scientist Croydon University Hospital 530 London Road Thornton Heath Surrey CR7 7YE Tel: 0208 401 3548 Fax: 0208 401 3189 ******************************************************************************************************************** This message may contain confidential information. If you are not the intended recipient please inform the sender that you have received the message in error before deleting it. Please do not disclose, copy or distribute information in this e-mail or take any action in reliance on its contents: to do so is strictly prohibited and may be unlawful. Thank you for your co-operation. 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ACB Web Site http://www.acb.org.uk Green Laboratories Work http://www.laboratorymedicine.nhs.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/ ------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 Green Laboratories Work http://www.laboratorymedicine.nhs.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/ ------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 Green Laboratories Work http://www.laboratorymedicine.nhs.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/ ------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 Green Laboratories Work http://www.laboratorymedicine.nhs.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/