What is the significance of a glomerular filtration rate of 43 mL/min/1.73 m² and how should it be managed?

GFR 43 mL/min/1.73 m²: Stage 3b Chronic Kidney Disease

A GFR of 43 mL/min/1.73 m² represents Stage 3b chronic kidney disease (moderately to severely decreased kidney function), which requires nephrology referral, intensive monitoring every 3-6 months, medication dose adjustments, blood pressure control with ACE inhibitors or ARBs, and preparation for potential renal replacement therapy. 1

Classification and Risk Stratification

• Stage 3b CKD is defined as eGFR 30-44 mL/min/1.73 m², indicating loss of approximately two-thirds of normal kidney function 1
• This stage carries substantially increased risks for cardiovascular disease, faster CKD progression, and mortality compared to earlier stages 2, 1
• Confirm chronicity by repeating eGFR within 3 months, as CKD requires persistent abnormalities for ≥3 months 1
• If creatinine-based eGFR appears discordant with clinical picture, measure cystatin C-based eGFR for confirmation, as creatinine estimates are inaccurate in 16-20% of individuals with eGFR <60 mL/min/1.73 m² 2, 1

Mandatory Nephrology Referral

Refer to nephrology immediately when eGFR <45 mL/min/1.73 m² (this patient at 43 mL/min/1.73 m² meets this criterion) 1

Additional referral triggers include:

• Confirmed proteinuria, especially UACR ≥300 mg/g 1
• Uncertainty about etiology of kidney disease 2, 1
• Rapidly progressing kidney disease 2, 1
• Difficult management issues 2, 1

Monitoring Schedule and Laboratory Testing

Check the following every 3-6 months for Stage 3b CKD: 2, 1

• Serum creatinine and eGFR
• Electrolytes (sodium, potassium, bicarbonate)
• Calcium and phosphorus 1
• Complete blood count (screen for anemia)
• Parathyroid hormone (PTH) every 6-12 months 1

Monitor at every clinic visit (minimum every 3 months): 2

• Blood pressure
• Body weight and nutritional status (serum albumin) 2

Measure urine albumin-to-creatinine ratio (UACR) at least annually to assess for albuminuria and monitor progression 1

Blood Pressure Management

Target blood pressure <130/80 mmHg 1

Use ACE inhibitor or ARB as first-line antihypertensive therapy, particularly if albuminuria is present 2, 1

Critical monitoring after initiating ACE-I/ARB:

• Check serum creatinine, eGFR, and potassium within 1 week of starting or dose escalation 2
• Do NOT routinely discontinue ACE-I/ARB at GFR <30 mL/min/1.73 m² as they remain nephroprotective 2, 3
• Temporarily suspend during intercurrent illness, IV radiocontrast administration, bowel preparation, or major surgery 2

Critical Medication Adjustments

Verify dosing of ALL medications, as many require adjustment when eGFR <60 mL/min/1.73 m² 1

Medications to AVOID or Use with Extreme Caution:

NSAIDs: STRICTLY AVOID 2, 1

• Reduce renal blood flow and can precipitate acute kidney injury
• Should not be used in patients taking ACE-I/ARB 2

Metformin:

• Review use when GFR <45 mL/min/1.73 m² 2
• Consider risk-benefit if GFR is stable
• Suspend if patient becomes acutely unwell 2

Dose Adjustments Required at This GFR Level:

Tetracyclines: Reduce dose when GFR <45 mL/min/1.73 m² (can exacerbate uremia) 2

Fluconazole: Reduce maintenance dose by 50% when GFR <45 mL/min/1.73 m² 2

Opioids: Reduce dose when GFR <60 mL/min/1.73 m² 2

Aminoglycosides: Reduce dose and/or increase dosage interval; monitor serum levels (trough and peak) 2

Dietary and Nutritional Management

Limit dietary protein to 0.8 g/kg body weight per day to reduce hyperfiltration injury and slow CKD progression 2, 1

Restrict sodium to <2 g/day to reduce blood pressure and maximize diuretic effectiveness 1

Monitor nutritional status every 3 months by measuring body weight and serum albumin 2

If malnutrition develops (unintentional weight loss >5% or albumin decrease >0.3 g/dL or <4.0 g/dL):

• Evaluate for causes 2
• Provide diet assessment and counseling by qualified personnel 2

Glycemic Control (if Diabetic)

Target A1C of 7% to delay CKD progression 1

Intensive glucose control has been shown to delay onset and progression of albuminuria and reduce eGFR decline in both type 1 and type 2 diabetes 1

Screening for CKD Complications

Screen for the following complications every 6-12 months: 1

• Volume status and fluid overload
• Electrolyte abnormalities (particularly hyperkalemia)
• Metabolic acidosis
• Anemia (check hemoglobin, iron studies)
• Mineral bone disease (calcium, phosphorus, PTH, vitamin D)

Cardiovascular Risk Management

Do not overlook cardiovascular risk, as CKD at this stage markedly increases cardiovascular disease risk, requiring aggressive risk factor modification 1

Monitor for dyslipidemias (triglycerides, LDL, HDL, total cholesterol) 2

Target LDL <100 mg/dL and non-HDL cholesterol <130 mg/dL 2

Statins are safe and recommended at this GFR level; no increase in toxicity for simvastatin 20 mg/day or simvastatin 20 mg/ezetimibe 10 mg combinations 2

Preparation for Renal Replacement Therapy

Begin discussing modality of RRT (hemodialysis, peritoneal dialysis, transplantation) with the patient 2

Provide structured education regarding preparation for RRT 2

If hemodialysis is planned:

• Preserve veins suitable for vascular access (avoid venipuncture in forearm veins) 2
• Consider referral for vascular access planning, though actual fistula creation typically occurs at lower GFR 2

If patient is willing to have renal transplant, initiate transplant evaluation 2

Hepatitis B vaccination is indicated early in patients likely to progress to end-stage kidney disease 1

Lifestyle Modifications

Encourage regular physical activity 2

• If unable to walk or increase physical activity, refer to physical therapy or cardiac rehabilitation 2

Encourage maintenance of employment and refer to vocational counseling per patient preference 2

Common Pitfalls to Avoid

• Do NOT rely on serum creatinine alone; always calculate and use eGFR 1
• Do NOT routinely discontinue ACE-I/ARB at this GFR level as they remain nephroprotective 2, 3
• Do NOT underestimate the severity of Stage 3b disease; despite being grouped under "stage 3," Stage 3b carries significantly higher risks than Stage 3a and warrants more aggressive monitoring 1
• Do NOT prescribe NSAIDs under any circumstances at this GFR level 2, 1
• Do NOT delay nephrology referral; this patient already meets criteria for specialist involvement 1