What investigations are included in a comprehensive workup for a patient with suspected Chronic Kidney Disease (CKD)?

CKD Workup Investigations

A comprehensive CKD workup requires measurement of serum creatinine with eGFR calculation, urine albumin-to-creatinine ratio (ACR), urinalysis with microscopy, and a complete metabolic panel as core initial tests, with additional investigations guided by clinical presentation and disease severity. 1

Core Laboratory Tests (Required for All Patients)

Kidney Function Assessment

• Serum creatinine to calculate estimated glomerular filtration rate (eGFR) using the 2021 CKD-EPI equation—this is the primary measure of kidney function 2, 1
• Cystatin C should be measured in adults with eGFR 45-59 mL/min/1.73 m² who lack markers of kidney damage when confirmation of CKD is required; if eGFR based on cystatin C is also <60 mL/min/1.73 m², CKD diagnosis is confirmed 2
• Blood urea nitrogen (BUN) to assess kidney function severity 3

Kidney Damage Assessment

• Urine albumin-to-creatinine ratio (ACR) on an early morning spot urine sample—this is the preferred method for detecting proteinuria and quantifying kidney damage 2, 1
• Confirm ACR ≥30 mg/g on a random sample with a subsequent early morning urine sample 2
• Urinalysis with microscopy to evaluate for casts, cells, and crystals that indicate underlying causes of CKD 3, 1

Electrolyte and Metabolic Panel

• Complete metabolic panel including sodium, potassium, calcium, phosphorus, magnesium, bicarbonate to identify electrolyte imbalances and metabolic acidosis 3, 1
• Parathyroid hormone (PTH) and phosphorus levels to assess mineral metabolism disorders, especially in advanced CKD (stages 3-5) 3

Additional Laboratory Tests Based on Clinical Context

Hematologic Assessment

• Complete blood count (CBC) to evaluate for anemia associated with CKD 1
• Consider erythropoietin levels in patients with anemia 4

Etiologic Workup

• Hemoglobin A1c for patients with diabetes or suspected diabetes 1
• Fasting lipid panel to assess cardiovascular risk 1
• Serologic testing for autoimmune diseases (ANA, ANCA, anti-GBM antibodies) when glomerulonephritis is suspected 1
• Complement levels (C3, C4) for suspected immune-mediated kidney disease 1
• Hepatitis B, C, and HIV serology when clinically indicated 1
• Serum and urine protein electrophoresis if multiple myeloma or monoclonal gammopathy is suspected 2, 1

Imaging Studies

Primary Imaging

• Renal ultrasound to assess kidney size, echogenicity, cortical thickness, rule out obstruction, and evaluate for structural abnormalities such as polycystic kidney disease 3, 1
• Small echogenic kidneys indicate chronic parenchymal disease 3

Additional Imaging When Indicated

• Doppler examination of renal vessels to exclude renovascular disease in patients with risk factors for vascular disease or renal artery bruits on examination 3
• Renal artery stenosis is found in approximately 4.3% of CKD patients and is potentially treatable 5

Monitoring Frequency

Baseline CKD (Stages 1-3a)

• Assess eGFR and albuminuria at least annually in all people with CKD 2
• More frequent monitoring (every 3-6 months) for individuals at higher risk of progression or when measurements will impact therapeutic decisions 2

Advanced CKD (Stages 3b-5)

• Monitor eGFR, electrolytes, and relevant parameters more frequently (every 3 months or more often) based on disease severity and stability 2, 3
• Repeat measurements beyond 3 months are required to confirm chronicity and distinguish CKD from acute kidney injury 1

Confirmatory Testing for Diagnosis

• Persistence of abnormalities for >3 months is required to diagnose CKD—this can be established through review of past measurements, imaging findings, kidney biopsy, or repeat testing 1
• Following detection of elevated ACR, hematuria, or low eGFR, repeat tests to confirm presence of CKD 1

Specialized Testing

Novel Biomarkers (Specialized Settings)

• NGAL, KIM-1, and IL-18 may be considered to detect kidney damage before serum creatinine changes, particularly in acute-on-chronic kidney injury 3

Kidney Biopsy

• Consider when the cause is unclear and results would guide treatment decisions, particularly for rapidly progressive disease, nephrotic syndrome, or suspected glomerular disease 1

Common Pitfalls to Avoid

• Do not rely on serum creatinine concentration alone—always calculate eGFR using validated equations 2
• Do not use the term "microalbuminuria"—laboratories should report ACR values with appropriate categories 2
• Confirm positive reagent strip tests with quantitative laboratory measurements expressed as a ratio to creatinine 2
• Recognize that small fluctuations in eGFR are common and not necessarily indicative of progression 2
• Consider non-albumin proteinuria when indicated—use specific assays for α1-microglobulin or monoclonal proteins 2