effective solute

Q: Which of the following is considered effective solute? (select one)

A) Glucose
B) Urea



Answer: A

Although this concept was determined six decades ago but still is very valid and clinically relevant. Glucose is considered an effective osmole because glucose osmotically shifts water from cells. In contrast, urea is an ineffective osmole since there is little or no water shift across the cells.

Clinical significance: Glucose osmotically shifts water out from the cells, expands the extracellular fluid volume, dilutes the sodium concentration and may give erroneously (pseudo) hyponatremia. This does not happen with a rise in urea concentration as there is little water shift.

#electrolytes 


References:

1. EDELMAN IS, LEIBMAN J, O'MEARA MP, BIRKENFELD LW. Interrelations between serum sodium concentration, serum osmolarity and total exchangeable sodium, total exchangeable potassium and total body water. J Clin Invest 1958; 37:1236. 

2.  Roscoe JM, Halperin ML, Rolleston FS, Goldstein MB. Hyperglycemia-induced hyponatremia: metabolic considerations in calculation of serum sodium depression. Can Med Assoc J. 1975;112(4):452–453.