What does a glomerular filtration rate (GFR) of 90 mL/min/1.73 m² indicate?

A GFR of 90 mL/min/1.73 m² Indicates Normal to High-Normal Kidney Function

A GFR of 90 mL/min/1.73 m² falls within the normal range and does not indicate kidney disease unless other markers of kidney damage are present. This value represents the threshold between CKD Stage 1 (≥90 with kidney damage) and Stage 2 (60-89 with kidney damage) in the classification system 1, 2.

Understanding the Classification

According to the most recent KDIGO 2024 guidelines, GFR categories are defined as follows 1, 2:

• G1: ≥90 mL/min/1.73 m² = "Normal to increased GFR"
• G2: 60-89 mL/min/1.73 m² = "Mildly reduced GFR"
• G3a: 45-59 mL/min/1.73 m² = "Moderately reduced GFR"
• G3b: 30-44 mL/min/1.73 m² = "Moderately reduced GFR"
• G4: 15-29 mL/min/1.73 m² = "Severely reduced GFR"
• G5: <15 mL/min/1.73 m² = Kidney failure

A GFR of 90 sits precisely at the boundary between normal and mildly reduced function, but is still considered within the normal range 3, 1.

Critical Context: GFR Alone Does Not Define CKD

The presence of chronic kidney disease requires both a reduced GFR (<60 mL/min/1.73 m²) OR evidence of kidney damage for ≥3 months 3, 4. At a GFR of 90, CKD would only be diagnosed if markers of kidney damage are present, such as:

• Albuminuria (albumin-creatinine ratio ≥30 mg/g)
• Abnormal urine sediment
• Structural abnormalities on imaging
• History of kidney transplantation

3, 4

Without these markers, a GFR of 90 mL/min/1.73 m² represents normal kidney function and does not warrant a CKD diagnosis.

Age-Related Considerations

Normal GFR values vary significantly by age 3, 5:

• Young adults (20-40 years): Normal GFR is approximately 107-130 mL/min/1.73 m² 3, 6
• After age 40: GFR declines by approximately 1% per year 5
• Age 70+: Values below 60 mL/min/1.73 m² may be considered physiologically normal 7

For a young adult, a GFR of 90 mL/min/1.73 m² may actually represent lower-than-expected function and warrants investigation for underlying causes 6. For an older adult (>60 years), this same value would be entirely appropriate 3, 5.

Clinical Implications and Risk Stratification

According to KDIGO risk categorization, a GFR of 90 with normal albuminuria (A1) represents low risk for adverse outcomes 1. However, risk increases if albuminuria is present:

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

1

Important Caveats About GFR Estimation

Estimated GFR (eGFR) has significant limitations at values ≥60 mL/min/1.73 m² 4, 8. The commonly used equations (MDRD, CKD-EPI) tend to underestimate true measured GFR at higher values 8, 9. Research shows that in healthy individuals, both equations significantly underestimate measured GFR, particularly when GFR is ≥90 mL/min/1.73 m² 8.

Clinical laboratories typically do not report eGFR as a specific numeric value above 60 mL/min/1.73 m² due to reduced accuracy in this range 4. When eGFR is reported as "90," interpretation depends heavily on:

• The specific equation used (CKD-EPI 2021 is preferred) 2, 10
• Patient age and muscle mass
• Presence or absence of albuminuria
• Clinical context

4, 2

Bottom Line

A GFR of 90 mL/min/1.73 m² indicates normal kidney function in most adults, particularly those over age 50. No intervention is required unless markers of kidney damage are present. For younger adults, this value may warrant further evaluation to ensure it represents true baseline function rather than early decline. The key is to assess for albuminuria and other markers of kidney damage—GFR alone does not define kidney disease at this level 3, 1, 2.