What laboratory tests are recommended for an adult patient with suspected renal failure and a history of diabetes, hypertension, or cardiovascular disease?

Laboratory Testing for Renal Failure

For adults with suspected renal failure and risk factors including diabetes, hypertension, or cardiovascular disease, obtain serum creatinine with eGFR calculation using the 2009 CKD-EPI equation, urine albumin-to-creatinine ratio (ACR) from a spot urine sample, complete blood count, serum electrolytes (sodium, potassium, chloride, calcium, phosphorus, bicarbonate), and blood urea nitrogen. 1, 2, 3

Core Blood Tests

Essential Markers of Kidney Function

• Serum creatinine is the primary marker for kidney function assessment and must be measured using a specific assay with calibration traceable to international standard reference materials 3
• Estimated GFR (eGFR) should be calculated from serum creatinine using the 2009 CKD-EPI equation rather than relying on serum creatinine concentration alone, as this detects chronic kidney disease more accurately 1, 2, 3, 4
• Blood urea nitrogen (BUN) helps calculate the BUN-to-creatinine ratio, which differentiates prerenal, intrinsic renal, and postrenal causes of acute kidney injury 2

Electrolyte Panel

• Serum electrolytes including sodium, potassium, chloride, calcium, phosphorus, and bicarbonate identify complications of kidney disease such as hyperkalemia, metabolic acidosis, and mineral bone disorder 1, 2, 3
• Complete blood count evaluates for anemia, a common complication of chronic kidney disease 1

Core Urine Tests

Proteinuria Assessment

• Urine albumin-to-creatinine ratio (ACR) from a first morning spot urine sample is the preferred method for detecting and quantifying proteinuria, as it is more sensitive and specific than urine dipstick 1, 2, 3
• The ACR is a continuous marker for cardiovascular event risk at all levels of kidney function, with risk starting at values consistently above 30 mg/g 1
• Urine sediment examination should be performed to detect abnormalities including cells, casts, and epithelial cells that help identify the specific cause of acute kidney injury 1, 3

Albuminuria Categories for Risk Stratification

• A1 (Normal to Mildly Increased): ACR <30 mg/g 1, 3
• A2 (Moderately Increased): ACR 30-299 mg/g 1, 3
• A3 (Severely Increased): ACR ≥300 mg/g 1, 3

GFR Categories for Disease Staging

The following GFR categories guide prognosis and management decisions 3:

• G1: ≥90 mL/min/1.73m² (normal or high, CKD only if kidney damage present)
• G2: 60-89 mL/min/1.73m² (mildly decreased, CKD only if kidney damage present)
• 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)

Monitoring Frequency Based on Disease Severity

For Chronic Kidney Disease

• Stage 3 CKD (eGFR 30-59 mL/min/1.73m²): Recheck every 6-12 months 2
• Stage 4 CKD (eGFR 15-29 mL/min/1.73m²): Recheck every 3-5 months 2
• Stage 5 CKD (eGFR <15 mL/min/1.73m²): Recheck every 1-3 months 2

For Patients on Specific Medications

• Serum potassium and creatinine should be rechecked within 1-2 weeks after initiating or adjusting doses of ACE inhibitors, ARBs, or diuretics, as these medications can cause hyperkalemia, hypokalemia, or acute kidney injury 2

Additional Tests in High-Risk Populations

For Patients with Diabetes

• Annual screening with serum creatinine and urine albumin testing is recommended for all patients with diabetes 1, 3
• Testing should begin at diagnosis for type 2 diabetes, or 5 years after diagnosis for type 1 diabetes 1

For Patients with Hypertension

• Initial evaluation should include serum creatinine with eGFR calculation and urine albumin-to-creatinine ratio 1
• Annual follow-up testing is recommended for those with initial normal results 1

Confirmatory Testing When Accuracy Is Uncertain

• Cystatin C should be considered as a confirmatory test when eGFR based on serum creatinine may be less accurate, such as in patients with extremes of muscle mass 3
• The combined creatinine-cystatin C equation provides improved accuracy in certain populations 3

Critical Interpretation Points

Acute Kidney Injury Superimposed on Chronic Disease

• A creatinine increase >50% from baseline or rapid eGFR decline indicates acute kidney injury superimposed on chronic disease, requiring immediate evaluation for reversible causes such as obstruction, volume depletion, or nephrotoxic medications 2

When to Refer to Nephrology

Specialist referral to nephrology is indicated when: 2

• eGFR <30 mL/min/1.73m² (Stage 4-5 CKD)
• Rapidly declining kidney function (eGFR decline >5 mL/min/1.73m² per year)
• Proteinuria with ACR >300 mg/g (severely increased albuminuria)
• Serum creatinine >2.5 mg/dL (>250 µmol/L)

Important Caveats

Diagnostic Confirmation

• A single abnormal test result is insufficient for diagnosis of chronic kidney disease; persistence of abnormalities for >3 months is required to distinguish CKD from acute kidney injury 3

Medication and Substance Interference

• Certain medications (such as trimethoprim and cimetidine) and substances can interfere with creatinine measurements, affecting eGFR accuracy 3
• Creatinine-based eGFR may be less accurate in patients with extremes of muscle mass, malnutrition, or amputation 1

Proteinuria Testing Pitfalls

• Urine dipstick does not detect small increases in urine albumin excretion and should not be used for screening; quantitative ACR measurement is required 1
• Confirmation with quantitative methods is necessary to avoid false-positive and false-negative results 3