Plasma Osmolality

High

Hyperglycemia Mannitol

Normal

Hyperproteinemia Hyperlipidemia Bladder irrigation

Low

Maximal volume of maximally dilute urine (<100 mosmol/kg)

ECF volume

Primary polydipsia Reset osmostat

Increased

Heart failure Hepatic cirrhosis Nephrotic syndrome Renal insufficiency

Normal

SIADH Exclude hypothyroidism Exclude adrenal insufficiency

Decreased

Urine Na+ concentration

<10 mmol/L

Extrarenal Na+ loss Remote diuretic use Remote vomiting

>20 mmol/L

Na+-wasting nephropathy Hypoaldosteronism Diuretic Vomiting

Yes

No