title: A proposed method for assessing plasma hypertonicity in vivo.
abstract: Indices of plasma hypertonicity, elevated plasma concentrations of solutes that draw fluid out of cells by osmosis, are needed to pursue hypertonicity as a possible risk factor for obesity and chronic disease. This paper proposes a new index that may be more sensitive to mild hypertonicity in vivo at a point in time than traditional measures. The index compares mean corpuscular volume (MCV) estimates from diluted (in solution by automated cell counter) and nondiluted blood (calculated from manual hematocrit, MCV=Hct/RBC*10(6)). A larger Auto vs Manual MCV (>2 fl) in vitro indicates hypertonicity in vivo if the cell counter diluent is isotonic with the threshold for plasma vasopressin (PVP) release and PVP is detectable in plasma (>0.5 pg/ml). To evaluate this principle of concept, hypertonicity was induced by 24-h fluid restriction after a 20 ml/kg water load in four healthy men (20-46 years). Unlike serum and urine indices, the MCV difference-&-PVP index detected hypertonicity in all participants.
authors.affiliation: Children's Hospital of Oakland Research Institute, Oakland, CA 94609, USA. jstookey@chori.org
authors.forename: J D
authors.initials: JD
authors.lastname: Stookey
authors.forename: M
authors.initials: M
authors.lastname: Burg
authors.forename: D E
authors.initials: DE
authors.lastname: Sellmeyer
authors.forename: J E
authors.initials: JE
authors.lastname: Greenleaf
authors.forename: A
authors.initials: A
authors.lastname: Arieff
authors.forename: L
authors.initials: L
authors.lastname: Van Hove
authors.forename: C
authors.initials: C
authors.lastname: Gardner
authors.forename: J C
authors.initials: JC
authors.lastname: King
mesh_terms: D000328:Adult; D003681:Dehydration / Q000175:diagnosis*; D004326:Drinking; D004909:Erythrocyte Indices; D006400:Hematocrit; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology / Q000209:etiology / Q000378:metabolism; D009994:Osmolar Concentration; D012307:Risk Factors; D014882:Water-Electrolyte Balance / Q000502:physiology*