Osmolality tests measure the amount of certain substances in blood, urine, or stool. These include glucose (sugar), urea (a waste product made in the liver), and several electrolytes, such as sodium, potassium, and chloride. Electrolytes are electrically charged minerals. They help control the amount of fluids in your body. The test can show whether you have an unhealthy balance of fluids in your body. An unhealthy fluid balance can be caused by many different conditions. These include excess salt intake, kidney disease, heart disease, and some types of poisoning.
Other names: serum osmolality, plasma osmolality urine osmolality, stool osmolality, osmotic gap