What serum sodium level is most likely to be found in an adult who lost water through sweating without replacing it?

When an adult loses water through sweating without replenishing it, this leads to a condition known as dehydration. As water loss occurs, the concentration of serum sodium can become elevated due to the relative decrease in total body water. Sodium is a key electrolyte in the body that helps maintain fluid balance, and when water is lost without adequate replacement, the serum sodium concentration can increase.

In this scenario, a serum sodium level of 155 mEq per liter suggests a significant increase in sodium concentration, indicative of hypernatremia, which is often a result of dehydration. This condition occurs when the water loss exceeds sodium loss, leading to a higher ratio of sodium to the available volume of water.

The levels indicated in other choices would signify varying degrees of normality or mild disturbances that are not typically associated with significant water loss through sweating alone. Therefore, the 155 mEq per liter level aligns with the physiological response to substantial water loss from sweating without proper hydration. This scenario effectively captures the body's adaptation to maintaining homeostasis under conditions of dehydration, resulting in increased serum sodium concentrations.