Osmolality, urine

Normal values:

• random specimen: 50 to 1400 mOsm/kg
• 12 to 14 hour fluid restriction: greater than 850 mOsm/kg

Note: mOsm/kg = milliosmoles per kilogram

What abnormal results mean:

Greater-than-normal measurements may indicate:

• Addison's disease (rare)
• congestive heart failure
• shock
• syndrome of inappropriate ADH secretion

Lower-than-normal measurements may indicate:

• aldosteronism (very rare)
• diabetes insipidus (rare)
• excess fluid intake
• renal tubular necrosis
• severe pyelonephritis

Additional conditions under which the test may be performed:

• complicated UTI (pyelonephritis)
• dilutional hyponatremia (SIADH)