Gauging fluid balance with osmolality

A measure of the concentration of particles, such as electrolytes, urea, and glucose in a solution, osmolality can help check the patient's fluid balance. The lab may use an osmometer to measure osmolality, but serum osmolality can be calculated from the patient's serum levels of sodium, blood urea nitrogen and glucose, while urine osmolality is commonly tested to determine the kidney's ability to concentrate urine.