Anion gap and osmolar gap (high): Difference between revisions

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==DDx==
==Calculations==
===Anion Gap===
AG = Na - (Cl  +  HCO3)
===Calculated Osm===
Calculated Osm = 2 x Na + (glu/18) + (BUN/2.8) + (ethanol/4.6) + (methanol/2.6) + (ethylene glycol/5) + (acetone/5.5) + (isopropanol/5.9)
*Normal = 275-295
===Osmolal Gap===
Osmolal Gap = measured osm - calculated osm
*Normal = (-)14-10 mOsm/L


==Differential Diagnosis==
===Toxicological===
*[[Methanol Poisoning|Methanol]]
*[[Ethylene Glycol Poisoning|Ethanol glycol]]
*[[Aspirin (Salicylate) Toxicity]]
*[[Iron Toxicity|Iron]]
*[[INH]]
*Paraldehyde
*[[Alcoholic Ketoacidosis]]
*Inhalants - [[CN]], [[CO]], [[Hydrogen Sulfide]]
*Toluene


TOXICOLOGICAL
===Non-Toxicological===
*[[Lactic Acidosis]]
*[[DKA]]
*[[Uremia]]


methanol
{{CAT MUDPILERS}}


ethanol glycol
==Evaluation==
{{Toxic Alcohols Anion/Osmolar Gaps}}


salicylates
==See Also==
*[[Osmolal or Osmolar Gap]]
*[[Anion Gap (High)]]
*[[Toxidromes]]


iron
==External Links==
*[http://www.mdcalc.com/serum-osmolality-osmolarity/ MDCalc - Serum Osmolality/Osmolarity]
*[http://www.mdcalc.com/anion-gap/ MDCalc - Anion Gap]


inh
==References==
<references/>


paraldehyde
[[Category:FEN]]
 
[[Category:Toxicology]]
alcoholic ketoacidosis
 
inhalants- CN, CO, H2S
 
toluene
 
 
NONTOX
 
lactic acidosis
 
dm ketoacidosis
 
uremia
 
 
MUDPILES
 
M- methanol
 
U- uremia
 
D- dka
 
P- paraldehyde
 
I- iron. inh
 
L- lactic acidosis
 
E- ethylene glycol
 
S- salicylates
 
 
 
 
 
==Source==
 
 
MISTRY 6/06
 
 
 
 
[[Category:Tox]]

Latest revision as of 05:31, 22 March 2026

Calculations

Anion Gap

AG = Na - (Cl + HCO3)

Calculated Osm

Calculated Osm = 2 x Na + (glu/18) + (BUN/2.8) + (ethanol/4.6) + (methanol/2.6) + (ethylene glycol/5) + (acetone/5.5) + (isopropanol/5.9)

  • Normal = 275-295

Osmolal Gap

Osmolal Gap = measured osm - calculated osm

  • Normal = (-)14-10 mOsm/L

Differential Diagnosis

Toxicological

Non-Toxicological


CAT MUDPILERS

Evaluation

Toxic Alcohols Anion/Osmolar Gaps

Substance Osmolar gap Metabolic acidosis Anion gap Ketones Ca Oxalate crystals Reduced vision Management
Ethanol + +/- (if ketoacidosis) +/- (if ketoacidosis) +/- - - Mainly supportive
Ethylene glycol + (early)* + + - + - Fomepizole, Thiamine, Pyridoxine, +/- Dialysis
Methanol + (early)* + + - - + Fomepizole or ethanol, Folinic acid/Folic acid, +/- Dialysis
Isopropyl alcohol + - - + (acetonemia without acidosis) - - Mainly supportive, +/- Dialysis if severe
Propylene glycol + + + (lactic acidosis) - - - D/C offending agent (e.g. IV lorazepam/diazepam), supportive, +/- Dialysis
  • Osmolar gap → Anion gap transition: For all toxic alcohols, the osmolar gap is elevated early (parent compound present) and decreases over time as the alcohol is metabolized into organic acid metabolites, which then produce an anion gap metabolic acidosis. A normal osmolar gap does NOT exclude toxic alcohol ingestion if presentation is delayed.
Key distinguishing features
  • Isopropyl alcohol: The only toxic alcohol that causes ketosis without metabolic acidosis (metabolized to acetone, not an organic acid)
  • Ethylene glycol: Ca oxalate crystals in urine + anion gap metabolic acidosis + renal failure
  • Methanol: Visual disturbances (blurred vision, "snowfield" vision, blindness) + anion gap metabolic acidosis + optic disc hyperemia on fundoscopy

See Also

External Links

References

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