From the Guidelines
To check for impaired renal function, you should get blood tests for serum creatinine and calculate the estimated glomerular filtration rate (eGFR) using the abbreviated MDRD formula, which is the most important indicator of kidney function, as it can detect mild impaired renal function even with normal serum creatinine values 1.
Importance of eGFR
The eGFR is a critical measure of kidney function, and values below 60 ml/min/1.73 m2 indicate chronic renal disease stage 3, whilst values below 30 and 15 ml/min/1.73 m2 indicate chronic renal disease stages 4 and 5, respectively 1.
Additional Tests
In addition to serum creatinine and eGFR, a urine test to measure albumin and creatinine levels, such as the albumin-to-creatinine ratio, can help detect early renal dysfunction and predict cardiovascular events 1.
Comprehensive Metabolic Panel
A comprehensive metabolic panel (CMP) is typically ordered, which includes tests for electrolytes like sodium, potassium, and phosphorus that can be affected by kidney problems 1.
Imaging Tests
Imaging tests such as ultrasound or CT scan might be recommended if structural issues are suspected, and regular testing is especially important if you have risk factors like diabetes, hypertension, heart disease, or a family history of kidney problems.
- Key points to consider:
- eGFR is the most important indicator of kidney function
- Urine tests, such as albumin-to-creatinine ratio, can help detect early renal dysfunction
- Comprehensive metabolic panel (CMP) is typically ordered
- Imaging tests may be recommended if structural issues are suspected
- Regular testing is crucial for early detection and intervention, especially in high-risk patients.
From the Research
Impaired Renal Function Tests
To check for impaired renal function, several tests can be used, including:
- Serum creatinine levels: This is a commonly used test to estimate glomerular filtration rate (GFR) 2, 3, 4, 5
- Serum cystatin C levels: This test has been shown to be a superior marker of rapidly reduced GFR compared to creatinine 3, 4
- Estimated GFR (eGFR) calculations: These calculations use serum creatinine and other factors to estimate GFR, but may be affected by inaccuracies in measured serum creatinine 5, 6
- Blood urea nitrogen (BUN) levels: These levels can be used in combination with creatinine levels to verify eGFR estimates 6
- Urine creatinine clearance (CrCl): This test measures the amount of creatinine cleared from the blood by the kidneys and can be used to estimate GFR 6
Considerations for Test Selection
When selecting a test for impaired renal function, several factors should be considered, including:
- Muscle mass: High muscle mass can affect serum creatinine levels and eGFR calculations 5
- Creatine supplementation: Ingestion of creatine can increase serum creatinine levels and affect eGFR calculations 5
- Blood urea nitrogen to creatinine ratio (BCR): A high BCR can cause misestimation of CKD stage 6
- Clinical data: Clinical data should be evaluated to identify reasons for differences in predicted GFRs using different equations 4