What investigations are recommended for patients suspected of having Chronic Kidney Disease (CKD)?

Investigations for Chronic Kidney Disease

All patients suspected of having CKD should be tested with both serum creatinine (with eGFR calculation) and urine albumin-to-creatinine ratio (ACR) as the essential initial investigations. 1

Essential Initial Laboratory Tests

Kidney Function Assessment

• Serum creatinine with eGFR calculation using the CKD-EPI equation is the recommended initial test for assessing glomerular filtration rate 1, 2
• If cystatin C is available, combine it with creatinine (eGFRcr-cys) for more accurate GFR staging in adults at risk for CKD 1
• eGFR should be reported rounded to the nearest whole number, with values <60 mL/min/1.73 m² reported as "decreased" 1

Albuminuria Assessment

• Urine albumin-to-creatinine ratio (ACR) on a spot morning urine sample is the preferred method for detecting kidney damage 1
• If ACR ≥30 mg/g is detected, confirm with a repeat early morning sample 1
• The term "microalbuminuria" should no longer be used 1

Establishing Chronicity (≥3 months duration)

Proof of chronicity can be established through: 1

• Review of past eGFR measurements or creatinine levels
• Review of past albuminuria or proteinuria measurements
• Imaging findings showing reduced kidney size (<9 cm) or cortical thinning 1
• Medical history of conditions known to cause CKD (diabetes, hypertension)
• Repeat measurements within and beyond the 3-month timepoint

Critical caveat: Do not assume chronicity based on a single abnormal eGFR or ACR, as this could represent acute kidney injury (AKI) or acute kidney disease (AKD) 1

Additional Diagnostic Investigations

Determining the Cause of CKD

The following tests should be used based on clinical context: 1

• Complete blood count to assess for anemia
• Electrolytes (sodium, potassium, bicarbonate, calcium, phosphate) to detect metabolic complications
• Fasting glucose or HbA1c to screen for diabetes
• Lipid panel (total cholesterol, LDL, HDL, triglycerides) for cardiovascular risk assessment 1
• Hepatitis B and C serologies in appropriate populations 1
• Complement levels, ANA, cryoglobulins if glomerulonephritis suspected 1
• Serum and urine protein electrophoresis if myeloma suspected 1

Imaging Studies

• Renal ultrasound should be considered to assess kidney size, structure, and exclude obstruction or stones 1
• Small kidneys (<9 cm) suggest advanced, irreversible disease 1
• Normal kidney size does not exclude CKD, particularly in diabetic nephropathy 2

Urine Microscopy

• Urine sediment examination to detect red blood cells, white blood cells, casts, or crystals that indicate specific kidney pathology 1

Advanced Testing When Indicated

• Kidney biopsy is suggested as a safe diagnostic test when the cause is unclear and results would guide treatment decisions 1
• Cystatin C measurement for confirmatory testing when eGFR based on creatinine is less accurate (e.g., extremes of muscle mass, eGFR 45-59 mL/min/1.73 m²) 1

Monitoring Frequency After Diagnosis

Once CKD is confirmed: 1, 2

• Assess eGFR and albuminuria at least annually in all CKD patients
• More frequent monitoring (every 3-6 months) for patients at higher risk of progression, including those with:
  • eGFR <30 mL/min/1.73 m² 3
  • Albuminuria ≥300 mg/24h 3
  • Rapid eGFR decline (>5 mL/min/1.73 m²/year) 1

High-Risk Populations Requiring Screening

Screen the following groups even if asymptomatic: 1, 4

• Age >60 years
• Diabetes mellitus
• Hypertension
• Cardiovascular disease
• Family history of CKD
• African American, Hispanic, Asian, Pacific Islander, or American Indian ethnicity
• HIV infection (especially with CD4 <200 or HIV RNA >4,000 copies/mL) 1
• Hepatitis C coinfection 1

Common Pitfalls to Avoid

• Do not rely on serum creatinine alone without calculating eGFR, as creatinine can be normal despite significantly reduced kidney function, particularly in elderly or low-muscle-mass patients 1, 5
• Do not use race-based eGFR equations; use the race-free CKD-EPI equation 1, 2
• Do not assume normal kidney function if eGFR is 60-89 mL/min/1.73 m² without checking for albuminuria or other markers of kidney damage 1, 2
• Confirm abnormal results before labeling a patient with CKD, as transient elevations in creatinine or albuminuria can occur with dehydration, exercise, urinary tract infection, or heart failure 1