CKD Stage for eGFR 37 mL/min/1.73 m²
An eGFR of 37 mL/min/1.73 m² corresponds to CKD Stage 3b, which is defined as moderate to severe decrease in kidney function with eGFR between 30-44 mL/min/1.73 m².
CKD Staging Classification
The internationally accepted staging system divides Stage 3 CKD into two subcategories based on eGFR thresholds 1:
- Stage 3a: eGFR 45-59 mL/min/1.73 m²
- Stage 3b: eGFR 30-44 mL/min/1.73 m² (your patient falls here)
- Stage 4: eGFR 15-29 mL/min/1.73 m²
- Stage 5: eGFR <15 mL/min/1.73 m² (kidney failure)
This subdivision of Stage 3 is clinically critical because Stage 3b patients demonstrate significantly higher risks of progression to end-stage renal disease and cardiovascular events compared to Stage 3a patients 2.
Critical Diagnostic Requirement
You must confirm chronicity before finalizing the CKD diagnosis. CKD requires abnormal kidney function persisting for at least 3 months to distinguish it from acute kidney injury 1, 3. Review historical eGFR measurements or repeat testing within 2-4 weeks if prior values are unavailable 4.
Essential Next Steps for Stage 3b CKD
Immediate Laboratory Assessment
Measure urinary albumin-to-creatinine ratio (UACR) immediately if not already done, as albuminuria classification is essential for risk stratification and determines treatment intensity 4, 3. The combination of eGFR 37 and UACR level determines your patient's progression risk:
- UACR <30 mg/g: Moderate risk
- UACR 30-300 mg/g: High risk
- UACR >300 mg/g: Very high risk—requires nephrology referral 4
Screen for CKD complications that emerge at this stage, including complete metabolic panel (sodium, potassium, bicarbonate, chloride), hemoglobin, serum calcium, phosphate, intact parathyroid hormone, and 25-hydroxyvitamin D 4. Patients progressing through Stage 3 manifest metabolic derangements (anemia, acidosis, mineral abnormalities) even when eGFR values appear similar to non-progressors 5.
Nephrology Referral Indications
Refer to nephrology immediately if any of the following are present 4, 3:
- UACR >300 mg/g (macroalbuminuria)
- Continuously increasing albuminuria despite optimal management
- Continuously decreasing eGFR
- Uncertainty about etiology or atypical features
- Difficulty managing CKD complications (anemia, mineral bone disease, metabolic acidosis)
- Resistant hypertension
Monitoring Frequency Based on Risk
Adjust monitoring intensity based on albuminuria level 4:
- Moderate risk (UACR <30 mg/g): Monitor eGFR and UACR 2 times per year
- High risk (UACR 30-300 mg/g): Monitor 3 times per year
- Very high risk (UACR >300 mg/g): Monitor 4 times per year and refer to nephrology
Common Pitfall to Avoid
Never rely on eGFR alone for diagnosis or risk assessment. Always measure UACR, as eGFR and albuminuria provide independent prognostic information for cardiovascular events, CKD progression, and mortality 4, 3. Approximately 48% of Stage 3 patients do not progress over 10 years, but macroalbuminuria increases progression risk 3-fold, microalbuminuria 2-fold, and Stage 3b classification itself increases risk 3-fold compared to Stage 3a 2.