Nephrology

Estimated Urine Osmolality

Estimates urine osmolality from urinalysis specific gravity.

Parameters

SG

Estimated Urine Osmolality Result

--
FormulaEstimated Urine Osmolality (mOsm/kg) = (Specific Gravity - 1.000) × 35,000

Clinical Pearls

Provides rapid diagnostic orientation during hyponatremia and hypernatremia workups before direct freezing-point depression osmometry results return.

Limitations

Large heavy molecules (radiocontrast dye, heavy proteinuria, severe glucosuria, mannitol) disproportionately raise specific gravity relative to true particle osmolality.