Lab Case 101 – Interpretation

An elderly man with critical illness, shock and hypoperfusion. His blood test shows:

High anion gap metabolic acidosis

Delta ratio = 1, pure AG metabolic acidosis

Appropriately compensated

corrected Na = Na + (Glucose-10)/3 = 168, patient has severe hypernatraemia (with pseudo hypernatraemia)

Renal failure – check previous, likely a component of acute on chronic

Corrected K for acidosis = 4.5, which is normal

Osmolality = 2XNa + Urea + Glucose = 356 mmol even without the urea result

Patient has all the features of HHS:

altered mental state

acidosis (NAGMA)

Pseudohypernatraemia

Glucose > 15 but not as high as expected with DKA

hyperosmolar state (>320)

in addition – elderly patient, but must check ketones

2.

HHS usually develops over a course of days to weeks, unlike diabetic ketoacidosis (DKA), which develops more rapidly, over the course of a few days. Often, a preceding illness results in several days of increasing dehydration. Adequate oral hydration may be impaired by concurrent acute illness (eg, vomiting) or chronic comorbidity (eg, dementia, immobility).

3.

Fluid – up to 9 litres deficit, give slowly after initial resuscitation, normal saline is ok as it is hyponatraemic with respect to the patient’s sodium

Monitor K an dreplace once below 4

Treat underlying cause

aim for normal pH, gluocose

 

 

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2 thoughts on “Lab Case 101 – Interpretation

  1. is it not the case that correcting the sodium involves adding a third of the glucose value rather than subtracting it? that would increase the calculated anion gap too.

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    • Correcting for pseudohyponatraemia involves adding a correction factor to the sodium. Correction factor, based on the glucose is (glucose-10)/3.
      Using the corrected sodium in anion gap calculations gives an erroneously high sodium which may then lead to an erroneously elevated anion gap.
      Interesting that this patient has a pseudohyponatraemia even though his sodium is elevated.
      Thanks for the comment, post has been updated

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