Which of the following is considered a pre-renal cause of azotemia?

Dehydration is indeed considered a pre-renal cause of azotemia because it leads to reduced blood volume and subsequently decreased renal perfusion. When the kidneys receive less blood flow, they may not be able to effectively filter waste products from the blood, resulting in an accumulation of nitrogenous waste, a condition known as azotemia. This situation occurs before any intrinsic kidney damage takes place, therefore categorizing it as a pre-renal cause.

Conversely, urethral obstruction is classified as a post-renal cause because it results from obstruction downstream of the kidneys, leading to increased pressure and potential damage to the renal tissues. Acute renal failure and chronic renal failure fall under intrinsic renal causes as they involve direct damage to the kidney tissues, affecting their ability to filter blood and excrete waste. Understanding these distinctions helps in diagnosing and treating azotemia based on its underlying cause.