Q: Why we multiply Na by 2 in the formula in calculated Plasma osmolalilty whose formula is 2 x Plasma Na (mEq/L) + [Glucose]/18 + Blood urea nitrogen(BUN)/2.8 ?
Answer:
The osmolal gap is calculated by subtracting the calculated serum osmolality from the measured serum osmolality.
High osmolal gap i.e., above 10 mOsm/kg signifies the presence of unmeasured osmoles, like alcohols (ethanol, methanol, isopropanol, or ethylene glycol.)
The formula for Calculated Posm = 2 x Plasma Na (mEq/L) + [Glucose]/18 + Blood urea nitrogen/2.8
Sodium is multiplied by 2 to count for accompanying anions - chloride and bicarbonate.
Glucose is divided by 18 and BUN is divided by 2.8 to convert units of mg/dL into mmol/L. Thats why the corrections for glucose and blood urea nitrogen are not required in countries that report labs in mmol/L.
#laboratory-scienr
#electrolytes
References:
1. Rose BD, Post TW. Clinical Physiology of Acid-Base and Electrolyte Disorders, 5th ed, McGraw-Hill, New York 2001. p.607.
2. DiNubile MJ. Serum osmolality (letter). N Engl J Med 1984; 310:1609.
3. García-Morales EJ, Cariappa R, Parvin CA, et al. Osmole gap in neurologic-neurosurgical intensive care unit: Its normal value, calculation, and relationship with mannitol serum concentrations. Crit Care Med 2004; 32:986.
No comments:
Post a Comment