What investigations should be done for a patient with an estimated Glomerular Filtration Rate (eGFR) of 42 indicating moderate Chronic Kidney Disease (CKD)?

Investigations for eGFR 42 (CKD Stage 3b)

For a patient with eGFR 42 mL/min/1.73 m², you must immediately measure urine albumin-to-creatinine ratio (UACR), review past creatinine values to confirm chronicity (>3 months), and screen for CKD complications including electrolytes, hemoglobin, calcium, phosphate, PTH, and vitamin D. 1

Confirm CKD Diagnosis and Chronicity

• Review historical eGFR measurements to determine if kidney dysfunction has persisted >3 months, which is required to confirm CKD diagnosis rather than acute kidney injury 1
• If duration is unclear or <3 months, repeat serum creatinine and eGFR within 2-4 weeks to distinguish CKD from AKI 1
• Measure UACR on a random spot urine sample immediately, as albuminuria classification is essential for risk stratification and treatment decisions 1
  • Normal: <30 mg/g (category A1)
  • Moderately increased: 30-300 mg/g (category A2)
  • Severely increased: >300 mg/g (category A3) 1
• If UACR is elevated (≥30 mg/g), confirm with 2 of 3 specimens collected within 3-6 months 1

Determine Underlying Cause

Evaluate the clinical context systematically to identify the etiology of kidney disease, as this guides treatment 1:

• Diabetes status: Check HbA1c if not recently measured, as diabetes is the leading cause of CKD and ESKD 2, 3
• Hypertension history: Document blood pressure control over time, as hypertension is both a cause and consequence of CKD 2, 3
• Medication review: Identify nephrotoxic exposures including NSAIDs, lithium, calcineurin inhibitors, and aminoglycosides 1, 2, 3
• Family history: Ask specifically about polycystic kidney disease, hereditary nephritis, and familial kidney disease 2
• Urinalysis with microscopy: Look for hematuria, pyuria, or casts that suggest glomerulonephritis or other primary kidney diseases 1

Consider atypical features requiring nephrology referral and possible biopsy 1:

• Absence of diabetic retinopathy in a diabetic patient (suggests non-diabetic kidney disease)
• Gross hematuria or dysmorphic red blood cells
• Rapid eGFR decline (>5 mL/min/1.73 m² per year)
• Nephrotic-range proteinuria (UACR >2200 mg/g)
• Active urinary sediment with cellular casts

Screen for CKD Complications

At eGFR 42 (stage G3b), complications become prevalent and require systematic screening 1:

Laboratory Tests (every 3-5 months for stage G3b) 1:

• Serum electrolytes: Detect hyperkalemia (especially if on ACEI/ARB) and metabolic acidosis 1
• Hemoglobin: Screen for anemia of CKD; if present, check iron studies (iron, ferritin, transferrin saturation) 1
• Serum calcium and phosphate: Detect mineral bone disease 1
• Intact PTH: Screen for secondary hyperparathyroidism 1
• 25-hydroxyvitamin D: Assess for vitamin D deficiency 1

Clinical Assessment (at every visit) 1:

• Blood pressure and weight: Monitor for hypertension (target <130/80 mmHg) and volume overload 1
• Volume status: Assess for edema, orthopnea, and signs of fluid retention 1

Risk Stratification and Monitoring Frequency

The combination of eGFR and albuminuria determines progression risk and monitoring intensity 1:

• eGFR 42 (G3b) with UACR <30 mg/g (A1): Moderate risk—monitor 2 times per year 1
• eGFR 42 (G3b) with UACR 30-300 mg/g (A2): High risk—monitor 3 times per year 1
• eGFR 42 (G3b) with UACR >300 mg/g (A3): Very high risk—monitor 4 times per year and refer to nephrology 1

Nephrology Referral Indications

Refer to nephrology if any of the following are present 1, 3:

• eGFR <30 mL/min/1.73 m² (though at 42, this threshold is not yet met)
• UACR ≥300 mg/g (severely increased albuminuria)
• Continuously increasing albuminuria despite treatment
• Rapid eGFR decline (>5 mL/min/1.73 m² per year)
• Uncertainty about etiology or atypical features suggesting non-diabetic kidney disease
• Difficulty managing CKD complications (anemia, mineral bone disease, hyperkalemia)

Common Pitfalls to Avoid

• Do not rely on serum creatinine alone—always calculate eGFR using validated equations (CKD-EPI 2021) 1
• Do not skip albuminuria testing—eGFR and UACR provide independent prognostic information for cardiovascular events, CKD progression, and mortality 1, 3
• Do not discontinue ACEI/ARB for creatinine increases <30% in stable patients, as this represents hemodynamic changes rather than kidney injury 1
• Do not assume diabetic kidney disease without confirming chronicity and excluding other causes, especially if atypical features are present 1, 4