What is the relationship between gastrointestinal (GI) bleeding and Blood Urea Nitrogen (BUN) levels?

From the Guidelines

Gastrointestinal bleeding is associated with elevated Blood Urea Nitrogen (BUN) levels, and the degree of elevation often correlates with the severity of bleeding, as supported by clinical predictors of increased risk for rebleeding or mortality, including elevated urea levels 1. The relationship between gastrointestinal (GI) bleeding and BUN levels is significant, as bleeding in the GI tract leads to the breakdown of blood proteins by digestive enzymes and bacteria, resulting in the release of amino acids that are absorbed and converted to urea by the liver. This process causes an increase in BUN levels without a proportional rise in creatinine, leading to an elevated BUN-to-creatinine ratio. Some key points to consider in this relationship include:

• The Blatchford score, which includes hemoglobin level, blood urea level, pulse, systolic blood pressure, and other factors, accurately identifies patients at low risk for clinical intervention and can be used to safely manage selected patients as outpatients without early endoscopy 1.
• Clinical predictors of increased risk for rebleeding or mortality, such as age greater than 65 years, shock, poor overall health status, and elevated urea levels, should be considered when evaluating patients with GI bleeding 1.
• The degree of BUN elevation often correlates with the severity of bleeding, with higher levels suggesting more significant hemorrhage.
• Other causes of elevated BUN, including dehydration, high-protein diet, corticosteroid use, and renal dysfunction, should be considered in the differential diagnosis.
• When evaluating a patient with an unexplained elevated BUN, especially with an increased BUN-to-creatinine ratio, clinicians should consider occult GI bleeding as a potential cause and perform appropriate diagnostic workup.

From the Research

Relationship Between Gastrointestinal (GI) Bleeding and Blood Urea Nitrogen (BUN) Levels

• The relationship between GI bleeding and BUN levels has been studied in various research papers 2, 3, 4, 5, 6.
• A study published in 2008 found that the BUN level at initial presentation is a weak predictor of the severity of nonvariceal upper GI bleeding as defined by ICU admission, but is not helpful in identifying patients with high-risk endoscopic lesions 2.
• Another study published in 2021 found that the blood urea nitrogen to serum albumin ratio (B/A ratio) is a significant predictor of ICU admission and in-hospital mortality in elderly patients with GI bleeding, and its prognostic performance is comparable to the AIMS65 score tool 3.
• A study published in 2017 found that an increase in BUN at 24 hours is a significant predictor of worse clinical outcomes, including inpatient death, rebleeding, and need for surgical or radiologic intervention, in patients with acute nonvariceal upper GI bleeding 4.
• A study published in 1990 found that the BUN/creatinine ratio can help distinguish upper from lower GI bleeding, with a ratio of greater than or equal to 36 suggesting upper GI bleeding 5.
• A study published in 2019 found that patients with upper GI bleeding have significantly elevated BUN levels while bleeding heavily, with a mean increase of 11.7 ± 7.2%, while patients with lower GI bleeding do not, with a mean increase of 4.2 ± 6.6% 6.

Predictive Value of BUN Levels

• BUN levels have been found to be a predictor of severity and outcomes in GI bleeding patients, including ICU admission and in-hospital mortality 2, 3, 4.
• The BUN/creatinine ratio has been found to be a useful tool in distinguishing upper from lower GI bleeding 5.
• BUN levels have been found to be elevated in patients with upper GI bleeding, particularly while bleeding heavily 6.

Clinical Implications

• The relationship between GI bleeding and BUN levels has important clinical implications, including the potential use of BUN levels as a predictor of severity and outcomes in GI bleeding patients 2, 3, 4.
• The BUN/creatinine ratio may be a useful tool in distinguishing upper from lower GI bleeding, which can inform clinical decision-making and management 5.
• Elevated BUN levels in patients with upper GI bleeding may indicate a more severe bleed and a higher risk of complications 6.