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urine osmolality

Normal range: 1) 50-1200 mosm/kg 2) with average fluid intake: 300-900 mosm/kg 3) after 12 hours of fluid restriction: > 850 mosm/kg 4) 24 hour urine: 300-900 mosm/kg Clinical significance: - urine osmolality - > 300 mOsm/kg in a patient with polyuria suggests osmotic diuresis - < 100 mOsm kg H2O suggests appropriately suppressed ADH - primary polydipsia - decreased solute intake (anorexia) [2,6] - > 100 mOsm kg H2O suggests ADH excess (SIADH) - elderly may not be able to dilute urine < 150 mOsm/kg H2O, thus - 150 mOsm kg H2O suggests decreased solute intake in the elderly [5] - > 150 mOsm kg H2O may suggest ADH excess (SIADH) in the elderly [5] Decreases: - diabetes insipidus - polydipsia Specimen: - stable at 4 degrees C for 24 hours Methods: - see osmolality

Related

serum osmolality

Specific

urine osmolal gap

General

osmolality (Osm) urine chemistry test

References

  1. Saunders Manual of Medical Practice, Rakel (ed), WB Saunders, Philadelphia, 1996, pg 1161
  2. Medical Knowledge Self Assessment Program (MKSAP) 11, 15, 19 American College of Physicians, Philadelphia 1998, 2009, 2022
  3. Clinical Guide to Laboratory Tests, 3rd ed. Teitz ed., W.B. Saunders, 1995
  4. Urine Osmolality Laboratory Test Directory ARUP: 20228
  5. Geriatric Review Syllabus, 11th edition (GRS11) Harper GM, Lyons WL, Potter JF (eds) American Geriatrics Society, 2022
  6. Berl T Impact of solute intake on urine flow and water excretion. J Am Soc Nephrol. 2008 Jun;19(6):1076-8. PMID: 18337482

Component-of

electrolyte/fluid management panel