Osmolal or osmolar gap: Difference between revisions

Latest revision as of 06:44, 22 March 2026

Definitions

Osmolarity = the total number of particles in solution per liter
Osmolality = the number of particles per kilogram of solvent

Calculations

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

External Links

References

Authors:

@@ Line 1: / Line 1: @@
 ==Definitions==
+*Osmolarity = the total number of particles in solution per liter
+*Osmolality = the number of particles per kilogram of solvent
-Osmolarity = the total number of particles in solution per liter
-Osmolality = the number of particles per kilogram of solvent
-== ==
-==Background==
-Serum osmolality should be measured by the freezing-point depression method rather than by the vapor pressure method, since the latter technique will underestimate the concentrations of volatile alcohols (methanol, ethylene glycol, and isopropanol).
 ==Calculations==
+===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
-Calculated Osm
+==Differential Diagnosis==
+*[[EtOH]]
-x Na + (glu/18) + (BUN/2.8) + (ethanol/4.6) +  (methanol/2.6) + (ethylene glycol/5) + (acetone/5.5) + (isopropanol/5.9)
+*[[Ethylene glycol]]
+*[[Methanol]]
+*[[Isopropyl alcohol toxicity]]
+*[[Diethylene glycol]]
-Osmolal Gap
+*[[Propylene glycol]]
+*[[Mannitol]]
-Measured osm - Calculated osm
+*Glycerol
+*Smaller gaps possible in:
-(Normal = (-)14-10 mOsm/L)
+**[[ketonemia|Ketoacidosis]]
+**[[Lactic acidosis]]
+**[[Chronic kidney disease]]
-Estimating Toxic Alcohol Concentration
-Toxic alcohol (mg/dL) = Osmolal gap x Conversion Factor
-*Parent compounds are responsible for the osmolar gap while their metabolites are responsible for anion gap changes
-==DDX (Increased)==
-Alcohols
-     -ethanol
-     -methanol
-     -ethylene glycol
-     -isopropanol
-Sugar
-     -glycerol
-     -mannitol
-Ketones
-     -acetone
-Other
-     -propylene glycol
-     -osmotic contrast dyes
+==See Also==
+*[[Anion Gap and Osmolar Gap (High)]]
+*[[Anion Gap (High)]]
+*[[Toxidromes]]
+==External Links==
+*[http://www.mdcalc.com/serum-osmolality-osmolarity/ MDCalc - Serum Osmolality/Osmolarity]
+*[http://www.mdcalc.com/anion-gap/ MDCalc - Anion Gap]
+==References==
+<references/>
 [[Category:FEN]]
+[[Category:Toxicology]]
+[[Category:Labs]]