Normally, the ratio of urea nitrogen to creatinine is between 10-20:1. If both urea nitrogen and creatinine are within the normal range, the ratio is not very meaningful. It is only when both are elevated at the same time that the ratio has greater significance. It is mainly used to identify the nature of oliguria. If the ratio of urea nitrogen to creatinine is greater than 10-20:1, it is considered to be prerenal oliguria, which is caused by a decrease in the amount of blood circulating in the kidneys due to various reasons, resulting in an increase in creatinine and urea nitrogen as well as a decrease in urine output. If the ratio is less than 10-20:1, it is considered to be renal or postrenal oliguria. Elevated urea nitrogen alone and normal creatinine can also lead to an elevated ratio, which is caused by decreased renal blood flow due to dehydration, excessive blood loss, heart failure, etc., or increased urea production due to gastrointestinal bleeding or eating large amounts of high-protein food.