Measure Uosm

• although useful for dx in limited circumstances, b/c almost always >300 Uosm <100 in ↑ H2O intake (1o polydipsia) or ↓ solute intake (beer potomania, “tea & toast”)

• Uosm >300 does not mean SIADH; must determine if ↑ ADH appropriate or inappropriate

• however, Uosm can be important when deciding on treatment (see below)