What laboratory value is indicative of dehydration?

Increased serum osmolality is a key laboratory value indicative of dehydration. During dehydration, the body loses more water than it takes in, leading to a higher concentration of solutes such as sodium, urea, and glucose in the serum. This results in an increase in serum osmolality, which is the measure of the body's electrolyte-water balance.

When dehydration occurs, the reduction in total body water results in a higher solute concentration because the same amount of dissolved particles is present in a smaller volume of fluid. Therefore, an increase in serum osmolality is a reliable indicator of dehydration in patients. This value helps clinicians assess the hydration status and guide further management of hydration therapies.

Other laboratory values may reflect various physiological responses to dehydration, such as low blood pressure and increased hematocrit, but they are not as direct indicators of the dehydration state itself as serum osmolality is.