What CKD stage does a 77-year-old man with an eGFR of 37 mL/min/1.73 m², serum creatinine 1.87 mg/dL, BUN 42 mg/dL and otherwise normal labs have?

CKD Stage Classification

Based on an eGFR of 37 mL/min/1.73 m², this 77-year-old man has Stage 3b chronic kidney disease (CKD). 1

CKD Stage Definition

The current KDIGO classification system defines CKD Stage 3b as an eGFR between 30-44 mL/min/1.73 m², which represents moderate to severe decrease in glomerular filtration rate. 1 This patient's eGFR of 37 mL/min/1.73 m² falls squarely within this range.

Critical Next Steps for Stage 3b CKD

Confirm Chronicity and Assess Albuminuria

• Verify that kidney dysfunction has persisted for at least 3 months by reviewing historical eGFR measurements, as this duration is required to distinguish CKD from acute kidney injury. 1, 2

• Measure urinary albumin-to-creatinine ratio (UACR) immediately on a random spot urine sample, as this is essential for risk stratification and treatment decisions. 1, 3 The combination of eGFR and albuminuria determines progression risk and monitoring intensity. 3

Identify Underlying Cause

• Evaluate for diabetes and hypertension as the primary causes, since diabetes accounts for 30-40% of CKD cases and hypertension is one of the most frequent causes in developed countries. 3, 2

• Review medication history for nephrotoxic exposures including NSAIDs, lithium, calcineurin inhibitors, and aminoglycosides. 3

• Assess for hematuria, pyuria, or casts in the urinalysis that would suggest glomerulonephritis or other primary kidney diseases. 3

Screen for CKD Complications

At Stage 3b, systematic screening for complications is mandatory: 3

• Electrolyte abnormalities: Monitor serum potassium (currently 4.0, normal), bicarbonate (currently 25, normal), and anion gap for metabolic acidosis
• Mineral bone disease: Measure intact parathyroid hormone (PTH), serum calcium (currently 9.1, normal), phosphate, and 25-hydroxyvitamin D, as PTH begins rising when eGFR falls below 60 mL/min/1.73 m² 3
• Anemia: Check hemoglobin, as anemia becomes increasingly prevalent at this stage
• Volume status: Assess blood pressure, weight, and signs of fluid retention 3

Risk Stratification and Monitoring

Monitoring Frequency Based on Albuminuria

The monitoring intensity depends critically on the UACR result: 3

• If UACR <30 mg/g (low risk): Monitor eGFR and UACR 2 times per year
• If UACR 30-300 mg/g (moderate risk): Monitor 3 times per year
• If UACR >300 mg/g (high/very high risk): Monitor 4 times per year and refer to nephrology

Nephrology Referral Indications

Refer to nephrology if any of the following are present: 3, 2

• eGFR <30 mL/min/1.73 m² (approaching Stage 4)
• Continuously increasing urinary albumin levels despite optimal management
• Continuously decreasing eGFR
• Uncertainty about etiology or atypical features suggesting non-diabetic kidney disease
• Difficulty managing CKD complications (hyperkalemia, metabolic acidosis, anemia, mineral bone disease)
• Resistant hypertension

Management Priorities for Stage 3b CKD

Blood Pressure Control

• Target blood pressure <130/80 mmHg for all CKD patients, particularly those with albuminuria. 3

• Initiate ACE inhibitor or ARB if UACR ≥300 mg/g regardless of blood pressure, or if UACR 30-299 mg/g with hypertension. 1, 3 These medications delay CKD progression and reduce cardiovascular events. 1

• Avoid combining ACE inhibitors with ARBs, as this increases adverse events without additional benefit. 3

Cardiovascular Risk Reduction

• Initiate statin therapy for cardiovascular risk reduction, as CKD patients have 5-10 times higher cardiovascular mortality risk than risk of progression to end-stage kidney disease. 2, 4

Protein Intake Restriction

• Recommend protein intake of approximately 0.8 g/kg/day in patients with diabetic kidney disease or CKD. 1

Avoid Nephrotoxins

• Discontinue NSAIDs and other nephrotoxic medications to prevent further kidney damage. 2

Clinical Context and Prognosis

Stage 3b CKD carries significant prognostic implications. In a prospective cohort study of referred CKD patients, those with Stage 3b had an annual probability of death of 6% and progression to Stage 4 of 22%. 5 The risk of cardiovascular disease is elevated, with a hazard ratio of 1.41 compared to those without CKD. 4

A recorded CKD diagnosis is associated with significant improvements in management practices and attenuated eGFR decline, with annual eGFR decline reducing from 3.20 mL/min/1.73 m² before diagnosis to 0.74 mL/min/1.73 m² after diagnosis. 6 Delayed diagnosis by 1-year increments is associated with elevated risk of progression to Stage 4/5 (hazard ratio 1.40) and kidney failure (hazard ratio 1.63). 6

Common Pitfalls to Avoid

• Do not rely on serum creatinine alone—always calculate eGFR using validated equations (CKD-EPI 2021). 3

• Do not skip albuminuria testing, as eGFR and UACR provide independent prognostic information for cardiovascular events, CKD progression, and mortality. 3

• Do not discontinue ACE inhibitors or ARBs for minor increases in serum creatinine (<30%) in the absence of volume depletion. 3

• Do not delay nephrology referral if eGFR continues to decline or approaches 30 mL/min/1.73 m², as timely referral improves outcomes. 3, 2