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?

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College Answer


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

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.