What does a glomerular filtration rate greater than 90 ml/min/1.73 m² indicate?

What Does a GFR >90 mL/min/1.73 m² Signify?

A GFR >90 mL/min/1.73 m² indicates normal to increased kidney filtration capacity, but this value alone does NOT rule out chronic kidney disease—you must also assess for markers of kidney damage such as albuminuria, hematuria, or structural abnormalities to determine if CKD is present. 1

Understanding GFR Categories

According to KDIGO nomenclature, GFR values are classified into distinct categories 1:

• G1 (GFR ≥90 mL/min/1.73 m²): "Normal to increased GFR"
• G2 (GFR 60-89 mL/min/1.73 m²): "Mildly reduced GFR"

The critical distinction is that stages G1 and G2 require evidence of kidney damage to diagnose CKD 2. A person with GFR >90 without any markers of kidney damage does not have CKD.

The Three-Component CKD Definition

CKD diagnosis requires at least 3 months of 2:

1. Structural/anatomical abnormalities (albuminuria, hematuria, imaging findings, pathological changes)
2. Functional impairment (reduced GFR)
3. Temporal persistence (≥3 months duration)

For GFR >90 to indicate CKD, you must document kidney damage markers, most commonly:

• Albuminuria (UACR ≥30 mg/g) 3
• Persistent hematuria or active urine sediment 4
• Structural abnormalities on imaging
• Pathological findings on biopsy

Risk Stratification When GFR >90

Even with normal GFR, risk varies dramatically based on albuminuria 1:

• G1A1 (GFR ≥90, UACR <30 mg/g): Low risk (green category)
• G1A2 (GFR ≥90, UACR 30-300 mg/g): Moderately high risk (yellow category)
• G1A3 (GFR ≥90, UACR >300 mg/g): High risk (orange category)

This heat map classification emphasizes that albuminuria severity, not just GFR, determines prognosis for cardiovascular events and CKD progression 1.

Clinical Pitfalls to Avoid

1. Assuming High GFR is Always Benign

While traditionally viewed as favorable, emerging evidence suggests extremely high GFR (hyperfiltration) may signal underlying pathology 5, 6. In diabetes, GFR ≥90 mL/min/1.73 m² with low albuminuria paradoxically increases kidney failure risk 5. However, this remains an area of active investigation and should not change routine clinical practice for most patients 1.

2. Ignoring Non-GFR Kidney Damage

In diabetes, up to 50% of patients with reduced kidney function have normal urinary protein levels 4. Conversely, significant albuminuria with preserved GFR still represents CKD and requires intervention 3.

3. Relying on Single Measurements

The temporal component requires persistence ≥3 months 2. Transient elevations in GFR (from volume expansion, high protein intake, or acute illness) should not be interpreted as permanent kidney status.

Practical Clinical Approach

When you encounter GFR >90 mL/min/1.73 m²:

1. Check for albuminuria using spot UACR 3
2. Examine urine sediment for hematuria or casts 4
3. Review imaging if available for structural abnormalities
4. Assess duration - confirm findings persist ≥3 months 2
5. Consider context:
   • In diabetes >5 years duration with retinopathy: likely represents early diabetic kidney disease if albuminuria present 4
   • In young healthy adults with isolated GFR >90 and no damage markers: normal kidney function
   • In patients with GFR >120 mL/min/1.73 m²: consider hyperfiltration, especially in diabetes 1

Special Populations

In children and adolescents >2 years, an eGFR <90 mL/min/1.73 m² should be flagged as "low" 7, reflecting different normal ranges in pediatric populations.

In diabetes, the presence of other microvascular complications (retinopathy, neuropathy) and disease duration >5 years supports diabetic kidney disease even with preserved GFR if albuminuria is present 4.