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serum osmolality
Reference interval:
1) 275-295 mosm/kg, age <= 60 years (adults & children)
2) 280-301 mosm/kg, age >= 61 years (elderly)
Clinical significance:
1) physiology
a) thirst is normally triggered by serum osmolality of > 290 mosm/kg
b) the organum vasculosum lamina terminalis is a chemoreceptor zone in the brain that senses osmolality
c) ADH is released from the hypothalamus when the plasma osmolality is > 280 mosm/kg
- plasma ADH levels zero for osmolality < 280 mosm/kg
- plasma ADH levels linearly related to osmolality for values > 280 mosm/kg
1) pathology
a) an osmolal gap > 10 mOsm/L may be secondary to various toxins (see osmolal gap)
b) normal osmolal gap, however does not rule the presence of a toxin
Increases:
- dehydration
- hypersomolar nonketotic diabetic coma
- diabetic ketoacidosis
- diabetes insipidus
- tube feeding
Decreases:
- adrenal insufficiency
- hypopituitarism
- water intoxication (polydipsia)
- postoperative states
- SIADH
Methods:
- see osmolality
Related
serum osmolal gap
urine osmolality
General
osmolality (Osm)
References
- Saunders Manual of Medical Practice, Rakel (ed), WB Saunders,
Philadelphia, 1996, pg 1161
- Medical Knowledge Self Assessment Program (MKSAP) 11, 15,
American College of Physicians, Philadelphia 1998, 2009
- Clinical Guide to Laboratory Tests, 3rd ed. Teitz ed.,
W.B. Saunders, 1995
- Osmolality
Laboratory Test Directory ARUP: 20046
Component-of
coma panel
electrolyte/fluid management panel