From the Guidelines
The primary blood tests for assessing kidney function, specifically evaluating for impaired renal function, are the estimated glomerular filtration rate (eGFR) and serum creatinine levels, which are typically part of a comprehensive metabolic panel that also includes blood urea nitrogen (BUN) and electrolyte levels. These tests are crucial in evaluating kidney function, as they measure how well the kidneys are filtering waste from the blood. According to the most recent guidelines, eGFR is calculated from serum creatinine levels and is used to assess kidney function, with normal values typically above 60 mL/min/1.73 m² 1.
To get an accurate eGFR, your healthcare provider will need your age, sex, and race, as these factors can affect creatinine levels. No special preparation is usually required for these tests, but fasting for 8-12 hours may be recommended for the most accurate results. The eGFR test measures how well your kidneys are filtering waste from your blood, with lower values indicating potential kidney disease or damage.
Some key points to consider when evaluating kidney function include:
- The eGFR test is typically part of a comprehensive metabolic panel that also includes blood urea nitrogen (BUN) and electrolyte levels.
- The test measures how well your kidneys are filtering waste from your blood, with normal values typically above 60 mL/min/1.73 m².
- Lower values may indicate kidney disease or damage, and additional tests or monitoring may be recommended if results are abnormal.
- The frequency of testing may vary depending on individual factors, such as known kidney issues, diabetes, or high blood pressure, with more frequent testing recommended for those at higher risk 1.
Overall, early detection of kidney problems through these blood tests can lead to more effective treatment and better long-term outcomes, emphasizing the importance of regular kidney function assessments, particularly for individuals with risk factors such as diabetes or hypertension 1.
From the Research
Blood Tests for Kidney Function
The following blood tests are used to assess kidney function and evaluate for impaired renal function:
- Serum creatinine concentration: This is a commonly used test to estimate glomerular filtration rate (GFR) and assess kidney function 2, 3, 4, 5.
- Cystatin C: This test can be used as a confirmatory test to assess kidney function, especially in individuals with variation in muscle mass or diet 2, 5.
- Urea: This test can be used in conjunction with serum creatinine to assess kidney function and diagnose kidney disease 4.
- Kidney injury molecule-1 (KIM-1): This is a novel biomarker that has been suggested as a sensitive biomarker of renal function, but more research is needed to validate its diagnostic efficiency and application in clinical practice 4.
Estimating Glomerular Filtration Rate (GFR)
GFR can be estimated using various equations, including:
- The Modification of Diet in Renal Disease (MDRD) study equation: This equation is used to estimate GFR in adults and takes into account serum creatinine concentration, age, gender, and race 3.
- The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation: This equation is a race-free equation that can be used to estimate GFR in adults and is recommended by the National Kidney Foundation 5.
- The Cockcroft-Gault equation: This equation is used to estimate creatinine clearance, but it is not as accurate as other equations and is being replaced by race-free eGFR equations 5.