Ethylene Glycol/Methanol

Chemical Pathology

Notes

These agents are potentially very toxic and clinicians managing patients are encouraged to discuss cases where treatment with an antidote or extracorporeal treatment may be indicated with the poisons information service. Access TOXBASE and/or contact the National Poisons Information Service (NPIS) on Tel. 0844 892 0111.

• Ethylene glycol is a constituent of antifreeze, coolant, brake fluid products. Methanol is a constituent of solvents, antifreeze/windscreen wash.
• Ethylene glycol is rapidly absorbed from the gut and is metabolised to glycolaldehyde then to glycolic, glyoxylic and oxalic acids which are responsible for the majority of its toxic effects.
• Glycolic acid is cleared by the kidney and is largely responsible for the marked acidosis seen in severe cases.
• There is increasing evidence that calcium oxalate monohydrate crystals are the cause of cerebral oedema and renal failure.
• Patients will develop a high osmolar gap as they absorb the glycol over the first few hours. Thereafter, as the glycol is metabolised to acids, the osmolar gap will fall while the patient's anion gap will climb and acidosis worsens.
• A severely poisoned patient can present early with a normal anion gap and a normal pH or hydrogen ion concentration; however, their osmolar gap will be high.
• Early treatment with an antidote can prevent the production of toxic metabolites and prevent the rise in anion gap.
• Although plasma lactate may be increased, some blood gas analysers may erroneously report an elevated lactate which is in fact due to cross reactivity with metabolic products of the toxic alcohol.
• A high anion gap metabolic acidosis suggests that presentation is late and that a substantial amount of ethylene glycol has been metabolised. The high anion gap usually occurs as the serum bicarbonate falls with progressive development of metabolic acidosis.
• A high anion gap metabolic acidosis is not specific to ethylene glycol ingestion and can occur with toxic alcohol ingestion (e.g. methanol) or with other clinical conditions (e.g. diabetic or alcoholic ketoacidosis, renal failure, multi-organ failure).
• Absence of a high anion gap metabolic acidosis does not exclude the diagnosis if the presentation is early and an antidote may still be required. Acidosis only develops after some ethylene glycol has been metabolised.
• Methanol can be assayed on the same sample as ethylene glycol but this must be specified at the time of requesting.

Sample requirements

For adults and children, blood taken at least 2 hours post ingestion into a 2mL fluoride-oxalate tube

Storage/transport

Do not store. Send immediately to the laboratory.

Required information

Relevant clinical details including time and nature of suspected exposure.

Turnaround times

Requests for ethylene glycol/methanol must be first agreed with the duty biochemist.

Once agreed, samples will be sent for urgent analysis to the assaying laboratory (this may be Southmead Hospital, Bristol or City Hospital Birmingham depending on the availability of a toxicologist), with results available within 2 hours of sample receipt by the assaying laboratory.

The duty biochemist at Southmead Hospital or at Birmingham may be contacted and samples sent direct to the assaying laboratory as instructed by them but please also inform the local laboratory so that follow up samples can also be expedited.

Southmead Hospital contact details: contact the duty biochemist via North Bristol NHS Trust switchboard Tel 0117 9505050

City Hospital Birmingham contact details: contact the Consultant Clinical Biochemist via the SWBH switchboard Tel: 0121 554 3801. Link http://www.cityassays.org.uk/ethyleneglycol.html

Reference ranges

Not applicable.

Once initiated, an antidote should be continued until the plasma ethylene glycol concentration is less than 50 mg/L.

Further information

For healthcare professionals access TOXBASE link above.

Diethylene glycol analysis is only available at City Hospital Birmingham

Page last updated 12/02/2015