Osmolality Urine Test

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Latest Edit: Hector 2014-03-24 (EDT)

See Also Lab Tests

Urine osmolality is a measurement of the number of dissolved particles in the urine. It is considered to be a more accurate measurement of urine concentration than specific gravity is as specific granvity is dependent on the weight and density of particles in the urine. Osmolality can also be measured over a wider range than specific gravity.[1], [2]


  • Osmolality is used to evalutate the concentrating ability of the kidney.
  • This test can also be used to monitor fluid and electrolyte balance.
  • Osmolality plays a vital role in the workup of patients with renal disease, inappropriate Antidiuretic Hormone (ADH) secretion, and diabetes insipidus.
  • Urine osmolality is more easily interpreted when the serum osmolality is simultaneously measured.

Patient Preparation

  • preparation for a fasting urine specimen may require ingestion of a high-protein diet for 3 days before the test.

Clinical Implications


High levels indicate:

Low levels indicate:

  • Diabetes insipidus
  • Excess fluid intake
  • Renal tubular necrosis
  • Severe pyelonephritis

Associated Tests


  1. Pagana Kathleen D, Pagana Timothy J (1998) Mosby's Manual of Diagnostic and Laboratory Tests, Mosby, Inc
  2. Weatherby Dicken, Ferguson Scott (2002) Blood Chemistry and CBC Analysis: Clinical Laboratory Testing from a Functional Perspective, Bear Mountain