Blood Tests for Renal Failure Evaluation
For patients suspected of having renal failure, essential blood tests include serum creatinine, blood urea nitrogen (BUN), estimated glomerular filtration rate (eGFR), electrolytes, and urine albumin-to-creatinine ratio (ACR). 1
Core Laboratory Tests
- Serum creatinine - Primary marker for kidney function assessment that should be measured using a specific assay with calibration traceable to international standard reference materials 1
- eGFR calculation - Should be derived from serum creatinine using the 2009 CKD-EPI equation rather than relying on serum creatinine concentration alone 1
- Blood Urea Nitrogen (BUN) - Important marker of nitrogenous waste accumulation 2
- Electrolytes - Sodium, potassium, calcium, chloride, phosphorus, and magnesium to assess electrolyte imbalances 1, 3
- Acid-base parameters - Total CO2 or bicarbonate to evaluate metabolic acidosis 3
- Complete Blood Count (CBC) - To assess for anemia, which commonly develops in renal failure 3
Urine Tests
- Urine albumin-to-creatinine ratio (ACR) - Preferred method for assessing proteinuria from an untimed urine sample 1
- Urine sediment examination - To detect abnormalities including cells, casts, and crystals 1
Risk Stratification Tests
- Cystatin C - Consider as a confirmatory test when eGFR based on serum creatinine may be less accurate 1
- Combined creatinine-cystatin C equation - Provides improved accuracy in certain populations 1
Interpretation Framework
GFR Categories:
- G1: ≥90 ml/min/1.73m² (Normal or high)
- G2: 60-89 ml/min/1.73m² (Mildly decreased)
- G3a: 45-59 ml/min/1.73m² (Mildly to moderately decreased)
- G3b: 30-44 ml/min/1.73m² (Moderately to severely decreased)
- G4: 15-29 ml/min/1.73m² (Severely decreased)
- G5: <15 ml/min/1.73m² (Kidney failure) 1
Albuminuria Categories:
- A1: <30 mg/g (Normal to mildly increased)
- A2: 30-300 mg/g (Moderately increased)
- A3: >300 mg/g (Severely increased) 1
Special Considerations
- For patients with diabetes or hypertension, annual screening with serum creatinine and urine albumin testing is recommended 1
- The National Kidney Foundation recommends assessing risk for CKD in all patients and performing blood pressure measurement, serum creatinine testing, urine albumin testing, and examination of urine for erythrocytes and leukocytes in those at increased risk 1
- Laboratory values should be monitored at intervals based on GFR category and albuminuria category to assess progression 1
- Point-of-care testing for creatinine and urine albumin may facilitate earlier diagnosis in rural or remote locations 1
Important Caveats
- A single abnormal test result is insufficient for diagnosis of chronic kidney disease - persistence of abnormalities for >3 months is required 1
- Certain medications and substances can interfere with creatinine measurements, affecting eGFR accuracy 1
- Timing of blood sample processing can affect results, so standardized collection protocols should be followed 1
- In patients with acute kidney injury superimposed on chronic kidney disease, interpreting blood test results requires comparison to baseline values 1
- False-positive and false-negative results can occur with proteinuria testing, so confirmation with quantitative methods is essential 1