What is the management approach for a patient with impaired renal function, specifically an estimated glomerular filtration rate (eGFR) of 40?

Management of eGFR 40 mL/min/1.73 m²

An eGFR of 40 mL/min/1.73 m² represents Stage G3b chronic kidney disease requiring systematic screening for complications, medication adjustments, blood pressure control with RAAS blockade if albuminuria is present, and nephrology referral if etiology is uncertain or disease is progressing rapidly. 1

CKD Classification and Risk Profile

• This eGFR level indicates moderately to severely decreased kidney function (Stage G3b CKD), which carries substantially increased risks for cardiovascular disease, CKD progression, and mortality 1
• The patient retains approximately 40% of normal kidney function, placing them at a critical juncture where aggressive intervention can prevent progression 1

Mandatory Screening for CKD Complications

Screen every 6-12 months for the following complications when eGFR <60 mL/min/1.73 m²: 1

• Blood pressure monitoring with target <130/80 mmHg 1
• Volume status assessment to detect fluid retention 1
• Electrolyte abnormalities (sodium, potassium, chloride, bicarbonate) 1
• Metabolic acidosis which accelerates bone disease and muscle wasting 1
• Anemia from reduced erythropoietin production 1
• Mineral bone disease (calcium, phosphorus, PTH, vitamin D) 1

Proteinuria Assessment and Blood Pressure Management

• Measure urine albumin-to-creatinine ratio (UACR) annually to quantify kidney damage beyond eGFR alone 1
• If albuminuria is present, initiate ACE inhibitor or ARB as first-line antihypertensive therapy regardless of baseline blood pressure, as these agents provide kidney-protective effects beyond blood pressure reduction 1
• Monitor serum creatinine and potassium 1-2 weeks after starting RAAS blockade, as a creatinine increase up to 30% is acceptable and does not require discontinuation 1

Critical Medication Management

Review and adjust ALL medications, as many require dose modification when eGFR <60 mL/min/1.73 m²: 1

• Strictly avoid NSAIDs (ibuprofen, naproxen, ketorolac) as they reduce renal blood flow and can precipitate acute kidney injury even with short-term use 1
• Verify dosing of renally-cleared medications including antibiotics, antivirals, and oral hypoglycemics 1
• For gout management specifically at this eGFR level, allopurinol maximum dosage should be adjusted to creatinine clearance; if uric acid target cannot be achieved, switch to febuxostat or benzbromarone with or without allopurinol 2

Glycemic Control (If Diabetic)

• Target A1C of 7% to delay CKD progression, as intensive glucose control has been proven to delay onset and progression of albuminuria and reduce eGFR decline 1
• Adjust doses of metformin, SGLT2 inhibitors, and other glucose-lowering agents according to eGFR-specific recommendations 1

Dietary Modifications

• Limit dietary protein to approximately 0.8 g/kg body weight per day to reduce hyperfiltration injury and slow progression 1
• Restrict sodium to <2 g/day (approximately 5 g salt/day) to reduce blood pressure and proteinuria 1
• These dietary restrictions become increasingly important as eGFR declines 2

Nephrology Referral Indications

Refer promptly to nephrology if any of the following are present: 1

• Uncertainty about the etiology of kidney disease (no clear cause like diabetes or hypertension) 1
• Difficult management issues such as resistant hypertension, persistent hyperkalemia, or metabolic acidosis 1
• Rapidly progressing kidney disease (eGFR decline >5 mL/min/1.73 m² per year) 1

Monitoring Frequency

• Measure eGFR and UACR at least annually in stable patients 1
• Laboratory monitoring for complications every 6-12 months for Stage 3 CKD 1
• More frequent monitoring (every 3-6 months) is warranted if complications are present or disease is progressing 1

Preventive Care

• Hepatitis B vaccination is indicated early in patients likely to progress to end-stage kidney disease, as vaccine response diminishes with declining kidney function 1
• Ensure pneumococcal and annual influenza vaccination are up to date 1

Critical Pitfalls to Avoid

• Do not overlook cardiovascular risk, as CKD at this stage markedly increases cardiovascular disease risk and requires aggressive modification of all cardiovascular risk factors (lipids, blood pressure, smoking cessation, diabetes control) 1
• Do not assume eGFR is perfectly accurate; it represents a population average and may overestimate true GFR in patients with low muscle mass or underestimate in those with high muscle mass 3, 4
• Consider cystatin C-based eGFR or measured GFR if creatinine-based estimates seem discordant with clinical picture 2, 5