What can cause hypovolemic hyponatremia with urine sodium levels less than 10?

Hypovolemic hyponatremia with urine sodium levels less than 10 mmol/L typically occurs when there is a loss of volume leading to concentrated urine. In the case of dehydration, the body loses both water and sodium, but the compensatory mechanisms kick in to retain sodium. When the body perceives a state of hypovolemia—due to fluid loss from conditions such as excessive sweating, vomiting, diarrhea, or inadequate fluid intake—it responds by conserving sodium while still losing water.

In dehydration, the kidneys work to maintain blood volume and will reabsorb sodium to help with this process, which results in lower urine sodium levels, often below 10 mmol/L. This reflects the body's attempt to conserve sodium and maintain euvolemia despite a deficit in total body water.

In contrast, chronic kidney disease, excessive hydration, or kidney failure can lead to different pathophysiological mechanisms where urine sodium values may not reflect the same compensatory processes seen in dehydration. Thus, dehydration is the condition that aligns best with the scenario of hypovolemic hyponatremia accompanied by low urine sodium levels.