From the Guidelines
A BUN to creatinine ratio of 28 is indicative of impaired renal function, likely suggesting prerenal azotemia, and requires immediate attention to address the underlying cause, with a focus on rehydration and further medical evaluation. This elevated ratio may indicate dehydration, decreased kidney perfusion, gastrointestinal bleeding, or high protein intake 1. The normal range for the BUN/creatinine ratio is typically considered to be between 10-20, and a ratio of 28 is elevated above this range.
Key considerations in the interpretation of this ratio include:
- Dehydration or decreased kidney perfusion, which can cause a rise in BUN more quickly than creatinine, as BUN is reabsorbed in the tubules while creatinine is not 1
- Gastrointestinal bleeding, which can increase BUN levels due to the absorption of blood proteins
- High protein intake, which can also increase BUN levels
- Other medical conditions that may affect kidney function, such as hypertension, diabetes, or cardiovascular disease
Management of an elevated BUN/creatinine ratio should focus on addressing the underlying cause, with particular attention to rehydration if dehydration is suspected. Patients should increase fluid intake to 2-3 liters per day unless contraindicated by other medical conditions. Further medical evaluation is recommended to determine the specific cause, as this ratio alone does not provide a definitive diagnosis. Laboratory tests, including complete metabolic panel, urinalysis, and possibly imaging studies, may be needed to fully assess kidney function and identify any underlying conditions. If symptoms such as fatigue, decreased urination, or confusion are present, immediate medical attention is warranted.
From the Research
Significance of BUN to Creatinine Ratio
The Blood Urea Nitrogen (BUN) to creatinine (Cr) ratio is a useful indicator of renal function. A ratio of 28 may indicate impaired renal function, but its interpretation depends on various factors.
Interpretation of BUN to Creatinine Ratio
- A BUN to creatinine ratio of greater than 25:1 may indicate an extrarenal problem, such as dehydration or heart failure 2.
- A ratio of 10:1 may indicate renal failure, either acute or chronic 2.
- However, a study found that a BUN to creatinine ratio greater than 20 was associated with increased mortality in critically ill patients, regardless of the presence of renal failure 3.
- Another study found that the BUN to creatinine ratio was not a reliable parameter for distinguishing prerenal AKI from intrinsic AKI 4.
Clinical Implications
- A high BUN to creatinine ratio may be caused by various factors, including hypovolemia, congestive heart failure, septic or hypovolemic shock, and high-dose steroids 5.
- The ratio may also be influenced by the patient's age, with elderly patients more likely to have a higher ratio due to lower muscle mass 5.
- The presence of multiple factors contributing to the high ratio may indicate a worse prognosis, with high mortality rates observed in patients with severely disproportionate BUN to creatinine ratios 5.