Is proteinuria and elevated Urine Albumin-to-Creatinine Ratio (UACR) >30 alone diagnostic of Chronic Kidney Disease (CKD) or is a reduced estimated Glomerular Filtration Rate (eGFR) also required?

Proteinuria and CKD: Diagnostic Criteria and Relationship

Elevated UACR >30 mg/g alone is diagnostic of chronic kidney disease (CKD) even with normal eGFR, as it represents kidney damage according to established guidelines. 1

Diagnostic Criteria for CKD

CKD is diagnosed by the persistent presence of either:

• Kidney damage (most commonly albuminuria with UACR ≥30 mg/g) OR
• Reduced eGFR (<60 mL/min/1.73 m²)

Staging System

The National Kidney Foundation classification defines CKD stages as follows:

Stage	Description	GFR (mL/min/1.73 m²)
1	Kidney damage* with normal or increased GFR	≥90
2	Kidney damage* with mildly decreased GFR	60-89
3	Moderately decreased GFR	30-59
4	Severely decreased GFR	15-29
5	Kidney failure	<15 or dialysis

*Kidney damage is defined as abnormalities on pathological, urine, blood, or imaging tests 1

Albuminuria as Evidence of Kidney Damage

• Normal UACR is defined as <30 mg/g creatinine
• Increased urinary albumin excretion (≥30 mg/g creatinine) is considered evidence of kidney damage 1, 2
• Historically, UACR 30-299 mg/g has been called "microalbuminuria" and ≥300 mg/g "macroalbuminuria" 1

Important Considerations for Diagnosis

1. Persistence requirement: Due to high biological variability (>20%), two of three specimens of UACR collected within a 3-6 month period should be abnormal before confirming albuminuria 1, 2

2. Potential false positives: Exercise within 24h, infection, fever, congestive heart failure, marked hyperglycemia, menstruation, and marked hypertension may elevate UACR independently of kidney damage 1

3. Confirmation testing: For patients with eGFRcreat 45-59 mL/min/1.73 m² without albuminuria, cystatin C measurement is suggested to confirm CKD diagnosis 1

Risk Stratification

The combination of eGFR and albuminuria provides superior risk stratification for:

• CKD progression
• Cardiovascular events
• Mortality

Patients with both decreased eGFR and increased albuminuria have substantially higher risk of adverse outcomes than those with either abnormality alone 3.

Clinical Implications

• Patients with elevated UACR ≥30 mg/g but normal eGFR are classified as CKD Stage 1 if eGFR ≥90 or Stage 2 if eGFR 60-89 1
• These patients require:
  • Annual monitoring of eGFR and UACR 1, 2
  • Blood pressure control with ACE inhibitors or ARBs recommended for those with UACR 30-299 mg/g 1
  • More intensive monitoring for those with UACR ≥300 mg/g 1

Common Pitfalls to Avoid

1. Missing CKD diagnosis: Relying solely on eGFR can miss early kidney disease. Up to 20% of progressive kidney disease in type 1 diabetes would be missed by screening with eGFR alone 1

2. Overdiagnosis concerns: In older adults with mildly reduced eGFR (45-59 mL/min/1.73 m²) but without albuminuria, confirmation with cystatin C is recommended before diagnosing CKD 1

3. Inconsistent monitoring: Failure to confirm persistent albuminuria with repeat testing can lead to overdiagnosis 1, 2

4. Ignoring transient causes: Not accounting for conditions that temporarily elevate UACR can lead to false positives 1

In conclusion, proteinuria with UACR >30 mg/g is sufficient for CKD diagnosis even with normal eGFR, but persistence must be confirmed with repeat testing to establish the diagnosis.