Is an eGFR of 85 mL/min/1.73 m² with normal BUN and serum creatinine indicative of normal kidney function, and what follow‑up is recommended?

An eGFR of 85 mL/min/1.73 m² with normal BUN and creatinine represents mildly reduced kidney function (CKD Stage G2) and requires annual monitoring with both eGFR and urine albumin-to-creatinine ratio (UACR).

Understanding the Clinical Significance

Your patient's eGFR of 85 mL/min/1.73 m² falls into CKD Stage G2 (60-89 mL/min/1.73 m²), which indicates mildly decreased kidney function. 1, 2 While this is often considered "near-normal," it's important to recognize that normal GFR in young adults is approximately 120-130 mL/min/1.73 m² for men and 120 mL/min/1.73 m² for women 3. The fact that BUN and serum creatinine are within normal laboratory ranges does not exclude kidney disease—eGFR provides more sensitive detection of early kidney function decline 4.

Key Clinical Context

An eGFR of 85 mL/min/1.73 m² alone does not define CKD unless there is evidence of kidney damage present for ≥3 months. CKD requires either:

• eGFR <60 mL/min/1.73 m² (persistent for ≥3 months), OR
• Evidence of kidney damage (albuminuria ≥30 mg/g, imaging abnormalities, pathological findings) with any eGFR 2

Stage G2 CKD (eGFR 60-89) only qualifies as CKD if accompanied by markers of kidney damage 1, 5.

Immediate Action Required

Measure urine albumin-to-creatinine ratio (UACR) immediately if not already done. This is the critical missing piece of information. 2

• If UACR is <30 mg/g (normal) and there are no other markers of kidney damage: This represents normal kidney function for age, requiring only annual screening
• If UACR is ≥30 mg/g: This confirms CKD Stage G2A2 or higher, requiring specific interventions

Follow-Up Algorithm

If No Albuminuria (UACR <30 mg/g):

• Repeat eGFR and UACR annually 1, 2, 5
• Address cardiovascular risk factors aggressively (this eGFR level still carries increased CV risk) 6
• No nephrology referral needed at this stage 5, 7, 8

If Albuminuria Present (UACR ≥30 mg/g):

• Confirm with repeat UACR within 3-6 months (due to high biological variability >20%) 5
• Exclude temporary causes: recent exercise, infection, fever, menstruation, marked hyperglycemia 5
• If persistent albuminuria confirmed, initiate evidence-based CKD treatment:
  • ACE inhibitor or ARB if hypertensive 1, 2
  • SGLT2 inhibitor if diabetic (can use with eGFR ≥20) 2
  • Statin therapy for cardiovascular protection 2
• Annual monitoring of both eGFR and UACR 1, 5, 7

When to Refer to Nephrology

Nephrology referral is NOT indicated at eGFR 85 mL/min/1.73 m² unless:

• Rapid progression occurs (sustained decline >5 mL/min/1.73 m² per year) 7, 8
• Persistent proteinuria >1 g/day (UACR ≥60 mg/mmol or ≥600 mg/g) 8
• Unexplained hematuria or other features suggesting non-diabetic kidney disease 5, 7

The threshold for routine nephrology referral is eGFR <45 mL/min/1.73 m² (Stage G3b) or <30 mL/min/1.73 m² (Stage G4) depending on the guideline 3, 5, 8.

Critical Pitfalls to Avoid

1. Don't assume normal kidney function based solely on normal BUN and creatinine. These markers lag behind actual GFR decline and can remain "normal" until significant kidney function is lost 4.

2. Don't dismiss eGFR 60-89 as "normal" without checking for albuminuria. This is Stage G2, and if albuminuria is present, it represents established CKD requiring intervention 1, 2.

3. Don't order a single UACR and act on it immediately. Confirm abnormal results with repeat testing due to high biological variability 5.

4. Don't forget that eGFR equations can be inaccurate in extremes of muscle mass, acute illness, pregnancy, or immediately post-surgery 3. Consider cystatin C-based eGFR if accuracy is questioned 9.

5. Age matters but doesn't normalize reduced eGFR. While eGFR declines with age (approximately 0.75 mL/min/year), an eGFR <60 mL/min/1.73 m² remains predictive of adverse outcomes regardless of age and should not be dismissed as "normal aging" 6, 10.