From the Guidelines
The primary blood test for assessing kidney function, specifically evaluating for impaired renal function, is the estimated glomerular filtration rate (eGFR), which is calculated from a simple blood draw measuring serum creatinine levels, as recommended by the most recent guidelines 1. When evaluating kidney function, it is essential to consider the eGFR, as it indicates how well the kidneys are filtering waste, with a normal range typically above 90 mL/min/1.73 m².
- The eGFR is a critical component of kidney function assessment, and its calculation should preferably use a race-free CKD-EPI equation, as suggested by recent guidelines 1.
- Additional important tests include blood urea nitrogen (BUN) and electrolyte levels, particularly sodium and potassium, which collectively provide a comprehensive picture of kidney health and function.
- These tests are essential for early detection and management of kidney disease, allowing for timely intervention to prevent further kidney damage, and should be performed at least annually for those at risk of kidney disease, or more frequently if kidney problems are suspected or being monitored 1.
- Patients generally don't need special preparation for these tests, but should inform their healthcare provider about any medications they're taking, as some can affect the results.
- The definition of moderate-to-severe CKD requires an eGFR of <60 mL/min/1.73 m2 or albuminuria of ≥30 mg/g (≥3 mg/mmol), highlighting the importance of regular monitoring and timely intervention 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.