Definition : Clinical laboratory measuring instruments designed to determine a solution's osmotic pressure, a variable related to the particle concentration (i.e., osmolality) of an aqueous solution such as body fluid, including whole blood, plasma, serum, and urine. These readings are used to determine levels of solute concentrations that control the movement of solutes throughout body tissues. Two main types of osmometers (freezing point and vapor-pressure osmometers) intended to measure small-particle osmolality (i.e., crystalloids such as glucose or urea, ions such as sodium or chlorine) are available; osmometers intended to measure osmolality due to molecules of a greater mass (i.e., colloids) and particles with a mass greater than 30,000 atomic mass units (i.e., Daltons) such as serum proteins are also available (i.e., colloid osmometers, also known as oncometers). An abnormal ratio between the osmolality values for urine and serum can indicate renal disease, diabetes insipidus, or secretion of abnormal levels of antidiuretic hormone; water and electrolyte imbalances are also present in patients with acute poisoning and shock trauma.
UMDC code : 12842