From the Guidelines
Kidney function tests are primarily seen in laboratory results through measurements of blood urea nitrogen (BUN) and creatinine levels, which are typically included in a comprehensive metabolic panel (CMP). These values, along with the estimated glomerular filtration rate (eGFR) calculation, provide a comprehensive picture of kidney function. The eGFR calculation, derived from creatinine levels, age, gender, and race, is a more accurate assessment of kidney function, with values below 60 mL/min/1.73m² suggesting kidney disease 1. Urinalysis results, including the presence of protein (proteinuria) or blood (hematuria), are also important indicators of kidney damage. Electrolyte levels, such as sodium, potassium, calcium, and phosphorus, reflect the kidney's ability to maintain proper balance. Additionally, the albumin-to-creatinine ratio in urine samples can detect early kidney damage, especially in diabetic patients. These laboratory values should be interpreted together rather than in isolation, as they collectively provide a comprehensive picture of kidney function and can help identify acute kidney injury or chronic kidney disease. It is essential to note that clinical laboratories should report an estimate of GFR using a prediction equation in addition to reporting the serum creatinine measurement, as recommended by the National Kidney Foundation 1. Furthermore, autoanalyzer manufacturers and clinical laboratories should calibrate serum creatinine assays using an international standard to ensure accurate measurements 1. Overall, a comprehensive approach to interpreting laboratory results is crucial for accurately assessing kidney function and identifying potential kidney damage or disease. Key laboratory tests for assessing kidney function include:
- Blood urea nitrogen (BUN) and creatinine levels
- Estimated glomerular filtration rate (eGFR) calculation
- Urinalysis results, including proteinuria and hematuria
- Electrolyte levels, such as sodium, potassium, calcium, and phosphorus
- Albumin-to-creatinine ratio in urine samples.
From the Research
Location of Kidney Function Tests in Laboratory Results
Kidney function tests, such as blood urea nitrogen (BUN) and serum creatinine levels, are typically found in the laboratory results of patients undergoing assessment for renal function.
- These tests are considered "standard fare" in the assessment of renal function 2
- They are relatively low-cost, widely available in standard hospital laboratories, and easy to run 2
- The results of these tests are usually reported together, with the BUN to creatinine ratio providing valuable information for diagnosis 3
Reporting of Kidney Function Test Results
The laboratory results for kidney function tests typically include:
- Serum creatinine levels, which are considered a more accurate test of renal function than BUN levels 2
- BUN levels, which can be influenced by extra-renal factors 2
- The BUN to creatinine ratio, which can help differentiate between intrinsic renal disease and extrarenal causes of abnormal levels 3
- Estimated glomerular filtration rate (eGFR), which is calculated based on serum creatinine levels and provides an estimate of kidney function 4, 5