From the Guidelines
An increasing Blood Urea Nitrogen (BUN) in a heart failure patient typically indicates worsening kidney function due to decreased renal perfusion, as suggested by the 2013 ACCF/AHA guideline for the management of heart failure 1. This occurs because the failing heart cannot pump blood effectively to the kidneys, leading to reduced kidney blood flow and filtration. As kidney function declines, nitrogenous waste products like urea accumulate in the blood, causing BUN levels to rise. This finding often suggests worsening heart failure with fluid overload or decreased cardiac output. It may also indicate excessive diuretic therapy causing volume depletion and prerenal azotemia. Some key points to consider in the management of heart failure patients with increasing BUN include:
- Evaluating the patient's overall fluid status, as recommended by the 2009 focused update incorporated into the ACC/AHA 2005 guidelines for the diagnosis and management of heart failure in adults 1
- Adjusting heart failure medications as needed, such as ACE inhibitors or beta blockers, while being mindful of potential intolerance due to hypotension and/or worsening renal function 1
- Potentially modifying diuretic dosing to avoid excessive diuretic therapy, as cautioned by the clinical policy on critical issues in the evaluation and management of adult patients presenting to the emergency department with acute heart failure syndromes 1
- Considering other causes of rising BUN, including gastrointestinal bleeding, high protein diet, or use of certain medications like corticosteroids
- Assessing the BUN-to-creatinine ratio, as a ratio greater than 20:1 often suggests prerenal causes rather than intrinsic kidney disease
- Regular monitoring of both BUN and creatinine is essential in heart failure management to balance effective heart failure treatment with kidney function preservation, as emphasized by the ESC guidelines for the diagnosis and treatment of acute and chronic heart failure 2012 1.
From the Research
Increasing BUN in Heart Failure Patients
An increasing Blood Urea Nitrogen (BUN) in heart failure patients indicates a poor prognosis and is associated with adverse outcomes, including mortality and re-hospitalization 2, 3, 4. The following points summarize the key findings:
- An increase in BUN ≥20% during hospitalization for acute heart failure (AHF) predicts a poor outcome independently from renal function deterioration and decongestion 2.
- Baseline BUN is the renal index most strongly associated with in-hospital and 1-year mortality in hospitalized heart failure patients 3.
- Changes in BUN during hospitalization are a stronger predictor of postdischarge survival than changes in estimated glomerular filtration rate (eGFR) 4.
- An increase of ≥10 mg/dL in BUN during hospitalization is associated with worse 60-day survival rates 4.
Association with Renal Function and Mortality
The relationship between increasing BUN and worsening renal function (WRF) is complex:
- WRF is not always associated with a poor response to treatment in acute heart failure, and the development of WRF should not preclude diuresis in the absence of volume depletion 5.
- Higher admission BUN and increasing BUN during hospitalization are independently associated with a worse survival rate 4.
- The impact of heart failure medication on worsening renal function and outcome is significant, with high doses of loop diuretics potentially having detrimental effects, whereas spironolactone and beta-blockers may be protective in patients with WRF 6.
Clinical Implications
The findings suggest that:
- Monitoring BUN levels is crucial in heart failure patients, as increasing BUN is a strong predictor of adverse outcomes 2, 3, 4.
- Clinicians should be cautious when using high doses of loop diuretics in patients with significant WRF, as this may have detrimental effects 6.
- The use of spironolactone and beta-blockers may be beneficial in patients with WRF, as they may have protective effects 6.