Laboratory Tests for Suspected Renal Failure
For suspected renal failure, essential laboratory tests include serum creatinine, blood urea nitrogen, electrolytes, urinalysis with microscopy, and urine albumin-to-creatinine ratio. 1
Core Blood Tests
- Serum creatinine is the primary marker for kidney function assessment and should be measured using an assay with calibration traceable to international standard reference materials 1
- Estimated glomerular filtration rate (eGFR) should be calculated using the 2009 CKD-EPI equation rather than relying on serum creatinine concentration alone 1
- Blood urea nitrogen (BUN) should be measured alongside creatinine, with the BUN-to-creatinine ratio helping differentiate between prerenal, intrarenal, and postrenal causes 2, 3
- Complete electrolyte panel including sodium, potassium, calcium, chloride, phosphorus, and magnesium to evaluate electrolyte imbalances 1, 4
- Complete blood count to assess for anemia, which commonly accompanies renal failure 5
- Acid-base status assessment through serum bicarbonate levels, as metabolic acidosis is common with glomerular filtration rates below 20 mL/min 4
Urine Tests
- Urine albumin-to-creatinine ratio (ACR) from an untimed urine sample is the preferred method for assessing proteinuria 1
- Urinalysis with microscopy to detect cells, casts, and crystals, which can help differentiate between various causes of renal failure 1, 3
- Urine sodium concentration and fractional excretion of sodium (FENa) to differentiate between prerenal and intrarenal causes (FENa <1% suggests prerenal cause, while >1% indicates intrarenal damage) 6, 3
- Urine osmolality to assess concentrating ability of the kidneys 4
Additional Tests for Risk Stratification
- Cystatin C as a confirmatory test when eGFR based on serum creatinine may be less accurate 1
- The combined creatinine-cystatin C equation provides improved accuracy in certain populations 1
- Serum protein electrophoresis when multiple myeloma or other paraproteinemias are suspected 7
Imaging Studies
- Renal ultrasound should be performed to evaluate kidney size, echogenicity, and to rule out obstruction 8
- Unenhanced CT of the abdomen and pelvis may be useful for characterization of ultrasound-detected hydronephrosis and to determine the level and cause of obstruction 8
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
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
- In patients with acute kidney injury superimposed on chronic kidney disease, interpreting blood test results requires comparison to baseline values 1
- Iodinated contrast should be avoided in acute kidney injury unless there is an overriding clinical question that cannot be answered with an alternative imaging modality 8
- Normal-sized kidneys on imaging do not exclude chronic kidney disease, as renal size is initially preserved in diabetic nephropathy or infiltrative disorders 8
Monitoring Frequency
- Monitoring frequency should be guided by GFR category, albuminuria category, and rate of progression 1
- More frequent monitoring is warranted for patients with rapidly declining kidney function or those at higher risk for progression 1
- Annual screening with serum creatinine and urine albumin testing is recommended for patients with diabetes or hypertension 1