Urine Osmolar Gap Calculation Urine Osmolar Gap represents ammonium salts = Measured Urine Osmolality - (2 x Na + 2 x K + Urea/2.8) Urine Osmolar Gap / 2 < 150 -> RTA 1 and 4 Urine Osmolar Gap / 2 > 400 -> Look to the gut Joel Topf, MD FACP @kidney_boy #Urine #OsmolarGap #Diagnosis #Nephrology #Calculation