Definition : Osmometers designed for direct determination of the osmotic pressure (i.e., osmolality) in a solution that includes particles with a mass greater than 30,000 atomic mass units (i.e., Daltons), such as serum proteins. Colloid osmometers (also known as oncometers) measure osmotic pressure directly by subjecting the sample to a protein-specific osmotic cell; the analytical cell is made up of two chambers of fluid separated by a semipermeable membrane, which is permeable to water and small molecules (e.g., crystalloids, ions) and impermeable to large molecules (i.e., colloids). The clinical use for colloid osmometers is different from other osmometers; they are intended to measure the decrease in osmotic pressure due to decrease in protein concentration in a wide variety of body fluids (e.g., urine, serum, plasma, cephalospinal fluid, pleural fluid, peritoneal fluid) and consequently to measure the risk of edema (e.g., pulmonary edema), facilitating the management of intravenous fluid therapy.
Entry Terms : "Oncometers" , "Colloid Osmometers"
UMDC code : 12800