Which factor could lead to an increased specific gravity of urine?

An increased specific gravity of urine indicates that the urine is more concentrated, which typically occurs when there is less water available to dilute the substances in urine. Decreased water intake results in a higher concentration of solutes in the urine because the kidneys retain water to maintain hydration levels in the body. This leads to an increase in specific gravity due to the higher ratio of solutes compared to the volume of water present.

In contrast, increased fluid intake would dilute the urine, potentially lowering the specific gravity as the urine becomes more diluted with excess water. Isothenuria refers to urine with a specific gravity that is not influenced by hydration status and remains fairly constant, while psychoactive polydipsia involves excessive thirst and fluid intake, leading to more diluted urine and thus lower specific gravity. Therefore, decreased water intake properly correlates with an increase in urine specific gravity due to a higher concentration of solutes.