What is the difference between measured and calculated osmolality?

The difference between the measured and calculated osmolality values is called osmolal gap that is a clinically relevant parameter. The most suitable equation for calculating osmolality requires that the osmolal gap is close to zero or zero [1].

Why is there a discrepancy between the calculated and measured osmolality?

An increased osmolar gap may be due to the presence of mannitol, ethanol, methanol, ethylene glycol, or other substance. The calculated osmolarity will differ from the measured osmolality in specimens with high lipid (lipemic) or protein (e.g. myeloma) concentrations.

What is measured osmolality?

Osmolality is a measurement of the number of moles of dissolved particles per kg of solvent (for clinical purposes, water is the solvent). Osmolarity is a measure of the number of dissolved particles per liter of solution. For consistency, we will refer to these measurements as osmolality throughout this topic.

How do you calculate osmotic gap?

Stool osmotic gap is calculated as 290 mOsm/kg − 2 × (stool Na + stool K). 290 mOsm/kg is the presumed stool osmolality, and the measured concentration of sodium and potassium cations is doubled to account for the corresponding anions which must be present.

Why is osmolar gap important?

Measuring the osmolar gap is important when toxic alcohols ingestion is suspected. With both methanol and ethylene glycol, the alcohols are metabolized from an alcohol to an aldehyde, and ultimately to an acid. As such, shortly after an ingestion, the patient may have an osmolar gap without an anion gap.

What does high osmolar gap mean?

High unexplained osmolar gaps indicate the possible presence of a toxic compound other than ethanol (ethylene glycol, methanol, acetone, isopropanol, or propylene glycol).

Why is a osmolality test done?

A blood osmolality test, also known as a serum osmolality test, is most often used to: Check the balance between water and certain chemicals in the blood. Find out if you have swallowed a poison such as antifreeze or rubbing alcohol. Help diagnose dehydration, a condition in which your body loses too much fluid.

What is the purpose of measuring AG and the Osmol gap?

Methanol, ethylene glycol, and acetone are classic poisons that increase the osmolar gap and AG; measuring the osmolar gap can help narrow the differential diagnosis of high-AG acidosis.

What is osmolality calc test?

Osmolality is a test that measures the concentration of all chemical particles found in the fluid part of blood.

How do you calculate osmolar gap with ethanol?

The serum ethanol (mmol/L) was related to osmolal gap (mOsm/Kg) by the formula: Ethanol = 0.83 X osmolal gap.

What is osmolality calculation serum?

Calculated serum osmolality = (2 X serum [Na]) + [glucose, in mmol/L] + [urea, in mmol/L] Sodium is multiplied by two to take into account the accompanying anions, chloride and bicarbonate. Glucose and blood urea nitrogen are divided by 18 and 2.8, respectively, to convert units of mg/dL into mmol/kg.