# Question 22.3

A 45-year-old man is admitted unconscious to the Emergency Department. His electrolytes are as follows:

 Parameter Patient Value Normal Range Sodium 119* mmol/l 135 – 145 Potassium 5.5* mmol/l 3.2 – 4.5 Chloride 80* mmol/l 100 – 110 Bicarbonate <5* mmol/l 22 - 27 Urea 10* mmol/l 3.0 – 8.0 Creatinine 105 µmol/l 50 – 100 Glucose 13.0* mmol/l 3.0 – 6.0 Lactate 8.8* mmol/l <2 Measured osmolality 340* mOsm/kg 275 – 295 Urine ketones Negative

a)  What are the abnormalities?

b)  Give a possible diagnosis

c)  What further tests would you consider to elucidate the cause of the acid base disturbance?

a)  What are the abnormalities?

• Metabolic acidosis with increased anion gap (34 mmol) Increased osmolar gap (approx 85 mmol)
• Hyperosmolar hyponatraemia
• Hyperlactataemia
• Mild hyperglycaemia

b)  Give a possible diagnosis

• Toxic alcohol ingestion (eg methanol, ethylene glycol)
• Alcoholic ketoacidosis
• Formaldehyde ingestion
• DKA possible but osmolar gap in this case higher than expected for DKA

c)  What further tests would you consider to elucidate the cause of the acid base disturbance?

• Specific assays for methanol, ethylene glycol, alcohol
• Urinary calcium oxalate crystals (ethylene glycol)
• Formate level (metabolite of methanol)

## Discussion

This is a straighforward question about high osmolar gap high anion gap metabolic acidosis.

The anion gap is (119) - (80 + 5) = 34, or 39.5 when calculated with potassium
The delta ratio, assuming a normal anion gap is 12 and a normal bicarbonate is 24, would therefore be (34 - 12) / (24 - 5) = 1.15, making this a pure HAGMA.

There is also a high osmolar gap of 79 (340- (119x2 + 10+ 13))

Hyperosmolar hyponatremia is not asked about, but is still interesting as an aside.

The causes of a metabolic acidosis with a raised anion gap and a raised osmolar gap are numerous, and well discussed in the literature. Specifically, methanol and the other toxic alcohols are a common cause, and are dealt with in detail elsewhere.

Alcoholic ketoacidosis is mentioned as a differential, although the urinary ketones are absent from the scenario sample. This may be because beta-hydroxybutyrate, the major ketone in alcoholic ketoacidosis, is not detected by urine dipsticks (which look for acetone and acetoacetate).

## References

Smith SW, Manini AF, Szekely T, Hoffman RS.. Bedside detection of urine beta-hydroxybutyrate in diagnosing metabolic acidosis. Acad Emerg Med. 2008 Aug;15(8):751-6.

Kraut JA, Xing SX. Approach to the evaluation of a patient with an increased serum osmolal gap and high-anion-gap metabolic acidosis. Am J Kidney Dis. 2011 Sep;58(3):480-4.