What does osmolar gap tell you?

An osmolal gap greater than 10 mOsm/kg indicates the presence of abnormal, unmeasured osmotically active molecules. The most common cause of an elevated osmolar gap is ingestion of an alcohol, including ethanol, methanol, ethylene glycol, diethylene glycol, propylene glycol, and isopropanol (isopropyl alcohol).

What is normal osmolal gap?

Normal osmolal gap is 10-15. Metabolic acidosis with elevated osmolal gap indicates methanol and ethylene glycol ingestions.

How do you find the osmolar gap?

CALCULATION

  1. Calculated osmolarity = (2 x [Na+]) + [glucose] + [urea])
  2. Osmolar gap = Osmolality (measured) – Osmolarity (calculated)
  3. normal = < 10.
  4. note that is a pragmatic clinical aid – the units are different (osmolality =mOsm/kg and osmolarity = mOsm/L) so it doesn’t make mathematical sense!

Why is osmolar gap important?

An elevated osmolar gap indicates an unknown solute but does not identify it. It is important to follow-up and determine what substance (or substances) is responsible. As an example, consider the following situation: Consider a patient who has ingested ethanol as well as ethylene glycol or methanol.

What does a negative osmolar gap mean?

A negative result decreases the post-test probability of toxic alcohol exposure to 23%. This is where things get dicey. Based on a normal osmolal gap, there might be a temptation to say that toxic alcohol has been “excluded’ and therefore fomepizole isn’t needed.

What causes increased osmolality?

Osmolality increases when you are dehydrated and decreases when you have too much fluid in your blood. Your body has a unique way to control osmolality. When osmolality increases, it triggers your body to make antidiuretic hormone (ADH).

Can osmolal gap be negative?

Performance of the osmolal gap to detect toxic alcohols varies widely depending on the equation used and laboratory techniques. A recent study suggests that it might have a positive likelihood ratio of ~1.2-1.7 and a negative likelihood ratio of ~0.3-0.45.

What is osmolarity level?

Osmolality is a measure of how much one substance has dissolved in another substance. The greater the concentration of the substance dissolved, the higher the osmolality. Very salty water has higher osmolality than water with just a hint of salt.

What does it mean when osmolality is high?

“Osmolality” refers to the concentration of dissolved particles of chemicals and minerals — such as sodium and other electrolytes — in your serum. Higher osmolality means you have more particles in your serum. Lower osmolality means the particles are more diluted.

What is the difference between osmolarity and osmolality?

The term osmolarity refers to the number of particles of solute per liter of solution, whereas the term osmolality refers to the number of particles of solute per kilogram of solvent.

What causes a negative osmolar gap?

Osmolal gap may be increased by numerous factors including renal failure, ketoacidosis, shock, electrolyte abnormalities, and contrast dye. Performance of the osmolal gap to detect toxic alcohols varies widely depending on the equation used and laboratory techniques.