From the Research
In gastrointestinal (GI) bleeding, creatinine and Blood Urea Nitrogen (BUN) levels typically change due to several physiological processes, with BUN levels often rising disproportionately compared to creatinine, creating an elevated BUN-to-creatinine ratio. This occurs primarily because blood in the GI tract is digested, releasing proteins that are broken down into amino acids and then converted to urea in the liver, directly increasing BUN levels 1. Additionally, GI bleeding frequently causes hypovolemia (reduced blood volume), which decreases kidney perfusion and triggers increased water and sodium reabsorption. This reduced blood flow to the kidneys leads to decreased glomerular filtration rate, causing both BUN and creatinine to rise, though BUN typically increases more significantly. Dehydration from the blood loss further exacerbates these changes. The combination of blood protein digestion and reduced kidney function typically results in a BUN-to-creatinine ratio greater than 20:1, which can be a useful diagnostic clue for GI bleeding when combined with other clinical findings. Some studies suggest that a BUN-to-creatinine ratio of greater than 35 can predict upper GI bleeding with high probability 1. However, due to the low sensitivity, values less than 35 are not diagnostic. Key factors to consider include:
- The digestion of blood in the GI tract and its impact on BUN levels
- The effects of hypovolemia on kidney perfusion and function
- The role of dehydration in exacerbating changes in BUN and creatinine levels
- The potential use of the BUN-to-creatinine ratio as a diagnostic tool in GI bleeding. It is essential to consider these factors in the context of the patient's overall clinical presentation to accurately diagnose and manage GI bleeding. The most recent and highest quality study 1 supports the use of the BUN-to-creatinine ratio as a diagnostic tool, but also highlights its limitations. Therefore, a BUN-to-creatinine ratio greater than 35 can be used to predict upper GI bleeding, but should be interpreted in conjunction with other clinical findings.