What lab workup is recommended for a patient with suspected Chronic Kidney Disease (CKD)?

Lab Workup for Chronic Kidney Disease

The essential lab workup for suspected CKD requires serum creatinine with calculated eGFR using the CKD-EPI equation and urine albumin-to-creatinine ratio (ACR) on an early morning sample as the two core tests. 1, 2

Core Laboratory Tests

GFR Assessment

• Measure serum creatinine and calculate eGFR using a validated equation (CKD-EPI 2009 or newer) rather than relying on serum creatinine concentration alone 1
• Laboratories should use enzymatic assays for creatinine (not Jaffe method) with calibration traceable to international standards to minimize interference from drugs and other substances 1
• Report eGFR values <60 mL/min/1.73 m² as "decreased" 1, 2
• Add cystatin C measurement for confirmatory testing in adults with eGFR 45-59 mL/min/1.73 m² who lack other markers of kidney damage, or when creatinine-based eGFR may be inaccurate (extremes of muscle mass, malnutrition, amputation) 1, 3, 2

Albuminuria Assessment

• Measure urine albumin-to-creatinine ratio (ACR) on an early morning urine sample as the preferred first-line test 1, 2
• Alternative acceptable tests in descending order: urine protein-to-creatinine ratio, reagent strip urinalysis with automated reading 1, 2
• Confirm any ACR ≥30 mg/g (≥3 mg/mmol) with a repeat early morning sample to establish persistence 1, 2
• Laboratories should report ACR and protein-to-creatinine ratios (not concentrations alone) and avoid the outdated term "microalbuminuria" 1

Complete Metabolic Panel

• Electrolytes: sodium, potassium, chloride, bicarbonate to detect hyperkalemia and metabolic acidosis 3, 2, 4
• Calcium and phosphorus to assess for mineral metabolism disorders, particularly in eGFR <45 mL/min/1.73 m² 3, 2
• Blood urea nitrogen (BUN) to assess severity of kidney dysfunction 3

Additional Essential Tests

• Complete blood count (CBC) to screen for anemia, a common CKD complication requiring management 2, 4
• Urinalysis with microscopy to evaluate for casts, cells, and crystals that indicate underlying etiology 3, 2
• Parathyroid hormone (PTH) when eGFR <45 mL/min/1.73 m² to detect secondary hyperparathyroidism 3, 4

Imaging Studies

• Renal ultrasound to assess kidney size, echogenicity, rule out obstruction, and evaluate for structural abnormalities (small echogenic kidneys suggest chronicity; enlarged kidneys suggest polycystic disease or obstruction) 3, 2
• Doppler examination of renal vessels if renovascular disease is suspected based on clinical risk factors 3

Establishing Chronicity

• Review past measurements to determine if kidney dysfunction has persisted >3 months, which is required to diagnose CKD rather than acute kidney injury 1, 4
• If duration is unclear, repeat testing in 3 months to confirm chronicity 1

Monitoring Frequency

• Annual assessment of eGFR and albuminuria for all patients with confirmed CKD 1, 2
• More frequent monitoring (every 3-6 months) for higher-risk patients: eGFR 30-44 mL/min/1.73 m² (stage 3b), eGFR <30 mL/min/1.73 m² (stages 4-5), or ACR ≥300 mg/g 1, 2, 4
• Increase monitoring frequency when initiating therapies that affect kidney function (ACE inhibitors, ARBs, SGLT2 inhibitors) 1

Clinical Context Assessment

• Evaluate personal and family history, medications (especially nephrotoxins like NSAIDs), social and environmental exposures to determine CKD etiology 1
• Risk stratification using both GFR category and albuminuria category determines prognosis and guides treatment intensity 1, 4

Common Pitfalls to Avoid

• Never rely on serum creatinine alone without calculating eGFR, as creatinine varies with age, sex, and muscle mass and misses early CKD, especially in elderly or thin patients 1, 5
• Do not skip albuminuria testing even in patients already on ACE inhibitors/ARBs, as the degree of proteinuria provides critical prognostic information beyond treatment decisions 1
• Recognize that eGFR accuracy is limited when GFR is near-normal (>60 mL/min/1.73 m²), in extremes of body size, or with rapidly changing kidney function 1
• Understand biological variability: expect 10-20% fluctuation in eGFR and ACR from non-pathologic causes before concluding true progression 1