The ratio of creatinine to urea nitrogen is usually expressed clinically as the ratio of blood urea nitrogen to creatinine, and the normal reference range is 15-24 to 1. When the ratio of blood urea nitrogen to creatinine is higher than the normal reference range ratio, that is, the serum urea nitrogen is increased more significantly than creatinine, which is commonly seen in patients with renal insufficiency, excessive protein intake, and retention of urea nitrogen due to gastrointestinal bleeding. A decrease in the ratio of blood urea nitrogen to creatinine is usually seen in patients with severe tubular damage, reduced urea nitrogen production, peritoneal dialysis, and artificial kidney patients. Once the blood urea nitrogen to creatinine ratio is not in the normal reference range, patients can go to the hospital for consultation and further comprehensive examination.