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Unit Code 9257:
Osmolality, Body Fluid

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Method Description

Measurement of the freezing point of urine is the most widely used

principle in osmometers. The extent of lowering below 0 degrees C

(the freezing point of water) is a function of the concentration of

substances dissolved in the urine. By definition, 1 milliosmole per

kilogram lowers the freezing point 0.001858 degrees C. It has been

observed that one may cool water to as low as -40 degrees C and

still have liquid water provided that no ice crystals, dust or other

contaminants are present and that the water is not agitated (super-

cooling). Vigorous agitation results in rapid freezing  of the super-

cooled solution (seeding). When the solution freezes, it quickly

warms to its freezing point and the temperature remains constant

for a relatively long period of time. (In Clinical Diagnosis and

Management by Laboratory Methods. 20th edition. Edited by JB

Henry. Philadelphia, PA, WB Saunders Company, 2001)

Performing Laboratory Location

Rochester

Key