<prompt> Effective serum osmolality is:255-270 mosmL270-285 mosmL285-300 mosmL300-325 mosmL  <response>: Total osmolality 2x plasma glucose18 BUN2.8 Effective osmolality or tonicity 2x plasma glucose18 The in plasma is measured as the nitrogen in the urea molecule, or blood urea nitrogen BUN. Effective osmolality does not include BUN because urea is an ineffective osmole. If plasma is taken as 141 meqL; then 2 x 141 282. Considering the normal plasma glucose, Normal serum osmolality: would fall in the range 275 to 290 mOsmL. Effective serum osmolality:would be 270-285 mOsmL. 