From the Guidelines
A BUN/creatinine ratio of 42 is significant and warrants attention, despite the individual values being within normal limits, as it suggests possible pre-renal issues or early kidney dysfunction. This ratio is considerably higher than the normal range of 10-20, and according to the National Kidney Foundation practice guidelines for chronic kidney disease, serum creatinine concentration alone is not a reliable means to assess the level of kidney function 1. A BUN of 21 mg/dL, calculated from the BUN/creatinine ratio of 42 with creatinine of 0.5 mg/dL, is technically within normal limits, but the elevated ratio is a sensitive early indicator of developing kidney stress. Common causes of an elevated BUN/creatinine ratio include dehydration, gastrointestinal bleeding, high protein diet, or early kidney dysfunction.
- Possible causes of the elevated ratio should be investigated, such as:
- Dehydration
- Gastrointestinal bleeding
- High protein diet
- Early kidney dysfunction I recommend increasing fluid intake, temporarily reducing protein consumption, and scheduling follow-up testing within 1-2 weeks to monitor trends, as suggested by the guidelines for evaluating and managing kidney function 1. If the patient has symptoms like fatigue, decreased urination, or edema, more immediate medical evaluation is needed.
From the Research
BUN and Creatinine Levels
- The given BUN level is not provided, but a normal BUN is 10 to 20 mg/100 mL 2.
- The creatinine level is 0.5 mg/100 mL, which is slightly below the normal range of 0.6 to 1.2 mg/100 mL 2.
- The BUN/creatinine ratio is 42, which is higher than the normal range and may indicate an extrarenal problem 2.
Significance of BUN/Creatinine Ratio
- A BUN/creatinine ratio of greater than 25:1 may indicate an extrarenal problem 2.
- A ratio of 10:1 may indicate renal failure (acute or chronic) 2.
- The given ratio of 42 is significantly higher than the normal range and may be associated with worse prognosis in patients with acute heart failure 3.
- However, a low BUN/creatinine ratio (≤12) may predict histologically confirmed acute interstitial nephritis 4.
Clinical Implications
- Elevated BUN levels have been associated with mortality in critically ill patients admitted to ICU, even after correction for co-founders including renal failure 5.
- Abnormal basic metabolic panel findings, including BUN and creatinine, have important implications for nursing care 6.
- The BUN/creatinine ratio may be a useful parameter in assessing renal function and prognosis in various clinical settings 2, 3, 4.