Which features are indicative of pre-renal azotemia?

Pre-renal azotemia is primarily characterized by an increase in blood urea nitrogen (BUN) relative to serum creatinine, typically resulting from inadequate renal perfusion rather than intrinsic kidney disease. In cases of pre-renal azotemia, the kidneys respond to perceived low blood volume or reduced blood flow by reabsorbing more urea, which causes the BUN to rise more significantly than creatinine. This leads to an elevated BUN/creatinine ratio, which usually exceeds 20:1.

Additionally, in pre-renal azotemia, the urine sediment is often bland, meaning there are no significant findings such as casts or cellular elements that would suggest intrinsic kidney damage. The bland urine sediment supports the diagnosis of a functional renal response to a systemic issue rather than a primary kidney pathology.

Other options present various renal issues or responses that do not fit the profile of pre-renal azotemia. For instance, low BUN with high creatinine typically indicates a different kind of kidney issue, potentially post-renal obstruction or acute tubular necrosis rather than pre-renal. High urine output may suggest renal compensation or diuretic use but does not align with the common features of pre-renal azotemia, where