Final answer:
The BUN/Creatinine ratio typically increases in post-renal acute renal failure due to the obstructive process leading to greater reabsorption of BUN in comparison to creatinine, which is not reabsorbed as much.
Step-by-step explanation:
In cases of post-renal acute renal failure, the BUN/Creatinine ratio typically increases. This increase is a result of the obstruction to urine flow, which can be due to factors such as kidney stones, prostate enlargement, or tumors. Since urea (the substance measured as BUN – blood urea nitrogen) is reabsorbed, and creatinine is not, obstructive conditions tend to raise the BUN more than creatinine, thereby increasing the ratio.
Pre-renal causes, like dehydration, can also lead to an increased BUN/Creatinine ratio because they result in decreased renal perfusion and keen reabsorption of BUN. However, in intrinsic renal causes where the kidney tissue itself is damaged, the ratio may remain unchanged or increase less significantly compared to post-renal causes. Understanding the changes in the ratio can help clinicians differentiate between these different types of acute renal failure.