Interpretation of Laboratory Values
These laboratory values indicate excellent kidney function with no evidence of kidney disease, though the slightly elevated BUN/creatinine ratio of 24 suggests possible mild dehydration or decreased muscle mass. 1
Kidney Function Assessment
Your kidney function parameters demonstrate:
eGFR of 121 mL/min/1.73 m²: This represents Stage 1 kidney function (normal or increased GFR ≥90 mL/min/1.73 m²), indicating excellent kidney filtration capacity. 2
Serum creatinine of 0.55 mg/dL: This is below the typical normal range (0.6-1.0 mg/dL for women, 0.8-1.3 mg/dL for men), which commonly occurs with decreased muscle mass or lower body weight. 2, 1
BUN of 13 mg/dL: This falls within the normal range of 10-20 mg/dL, indicating appropriate nitrogen waste handling. 3
BUN/Creatinine Ratio Analysis
The BUN/creatinine ratio of 24 exceeds the normal range of 10:1 to 20:1, suggesting a pre-renal condition rather than intrinsic kidney disease. 3
Most Likely Explanations:
Mild dehydration: The most common cause of an elevated BUN/creatinine ratio when kidney function (eGFR) remains excellent. 1 Evaluate for clinical signs including dry mucous membranes, decreased skin turgor, and recent fluid intake history. 1
Low muscle mass: The low creatinine level (0.55 mg/dL) suggests reduced muscle mass, which is particularly common in older adults, sedentary individuals, or those with chronic illness. 2, 1 This lowers the denominator in the ratio calculation, artificially elevating the ratio even with normal BUN.
Clinical Significance
No kidney disease is present based on these values. The National Kidney Foundation guidelines define chronic kidney disease as either kidney damage markers (such as proteinuria) or eGFR <60 mL/min/1.73 m² for ≥3 months. 2 Your eGFR of 121 mL/min/1.73 m² is well above this threshold and indicates normal kidney function for a young adult (normal GFR in young adults is approximately 120-130 mL/min/1.73 m²). 2
Important Caveats
eGFR accuracy in low muscle mass: When muscle mass is significantly reduced (as suggested by your low creatinine), eGFR equations may overestimate true kidney function. 1 Consider cystatin C-based eGFR for more accurate assessment if clinical concern exists. 1
Serum creatinine limitations: Creatinine alone is an insensitive marker that doesn't significantly rise until GFR has decreased by at least 40%. 2 However, your elevated eGFR confirms this is not a concern in your case.
Recommended Actions
Address hydration status: Increase fluid intake if dehydration is suspected, then recheck BUN/creatinine ratio in 1-2 weeks. 1
Assess muscle mass: Clinical evaluation for sarcopenia or malnutrition if creatinine remains persistently low. 1
No specific kidney monitoring needed: With normal kidney function and no proteinuria, routine annual monitoring is sufficient unless other risk factors develop (diabetes, hypertension). 2