Laboratory Tests for Renal Insufficiency
The essential laboratory tests for diagnosing renal insufficiency include serum creatinine, estimated glomerular filtration rate (eGFR), blood urea nitrogen (BUN), urinalysis for proteinuria, and electrolytes. 1, 2
Core Laboratory Tests
- Serum creatinine is the primary marker for kidney function assessment and should be measured using a specific assay with calibration traceable to international standard reference materials 1
- Estimated glomerular filtration rate (eGFR) calculated using the 2009 CKD-EPI equation is preferred over relying on serum creatinine concentration alone 1
- Blood urea nitrogen (BUN) should be measured alongside creatinine, as the BUN-to-creatinine ratio helps differentiate between prerenal, intrinsic renal, and postrenal causes 2, 3
- Urinalysis with microscopy to detect proteinuria, hematuria, and cellular casts that may indicate kidney damage 4, 5
- Urine protein quantification using spot urine albumin-to-creatinine ratio (ACR) or protein-to-creatinine ratio (PCR) from a first morning sample 4, 1
- Electrolytes including sodium, potassium, chloride, calcium, phosphorus, and bicarbonate to evaluate electrolyte imbalances and acid-base status 2, 4
Interpretation Framework
GFR Categories (per KDIGO guidelines)
- G1: ≥90 mL/min/1.73m² (Normal or high GFR) 4
- G2: 60-89 mL/min/1.73m² (Mildly decreased GFR) 4
- G3a: 45-59 mL/min/1.73m² (Mildly to moderately decreased GFR) 4
- G3b: 30-44 mL/min/1.73m² (Moderately to severely decreased GFR) 4
- G4: 15-29 mL/min/1.73m² (Severely decreased GFR) 4
- G5: <15 mL/min/1.73m² (Kidney failure) 4
Albuminuria Categories
- A1: <30 mg/g (Normal to mildly increased) 4, 1
- A2: 30-300 mg/g (Moderately increased) 4, 1
- A3: >300 mg/g (Severely increased) 4, 1
Additional Tests Based on Clinical Context
- Cystatin C as a confirmatory test when eGFR based on serum creatinine may be less accurate (e.g., in elderly, malnourished patients, or those with reduced muscle mass) 1, 6
- Complete blood count (CBC) to evaluate for anemia, which commonly occurs in chronic kidney disease 5, 7
- Serum albumin to assess nutritional status and protein loss 2
- Renal ultrasound to evaluate kidney size and rule out obstruction in patients with evidence of CKD 4
- 24-hour urine collection for more precise measurement of protein excretion and creatinine clearance when needed 5
Special Considerations
- Elderly patients often have normal serum creatinine despite significant renal impairment due to decreased muscle mass; eGFR calculation is particularly important in this population 6, 8
- Patients with monoclonal gammopathies or multiple myeloma require specialized assessment including serum free light chain measurement, urine protein electrophoresis, and serum protein electrophoresis 4, 7
- HIV-infected patients should be screened with urinalysis for proteinuria and eGFR calculation, with annual follow-up for those at high risk 4
Important Caveats
- A single abnormal test result is insufficient for diagnosis of chronic kidney disease; persistence of abnormalities for >3 months is required 1
- Serum creatinine alone is an inadequate screening test for renal failure, particularly in elderly patients, leading to underdiagnosis 6, 8
- The BUN-to-creatinine ratio helps distinguish between causes of renal dysfunction: a ratio >20:1 suggests prerenal causes, while a ratio of approximately 10:1 is more typical of intrinsic renal failure 3
- Certain medications and substances can interfere with creatinine measurements, affecting eGFR accuracy 1
Monitoring Recommendations
- Patients with confirmed CKD should have monitoring frequency 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
- Patients with diabetes, hypertension, or other risk factors should undergo annual screening with serum creatinine and urine albumin testing 1, 9