eGFR: How to Interpret Your Result

What eGFR Actually Measures

Glomerular filtration rate is the volume of blood plasma your kidneys fully clear of a marker substance each minute, normalized to a body-surface area of 1.73 m². Because measuring true GFR requires an inulin infusion or iohexol clearance test, clinicians use the estimated version, calculated from routine serum creatinine plus age and sex.

The 2021 CKD-EPI Creatinine equation replaced the older MDRD formula and removed race as a variable after evidence showed race-based adjustments systematically underestimated CKD burden in Black patients. The National Kidney Foundation and the American Society of Nephrology formally endorsed this change in 2021 (1).

How the Calculation Works

The CKD-EPI 2021 equation uses serum creatinine (Scr), age, and sex assigned at birth. The general form is:

eGFR = 142 × (Scr/κ)^α × (0.9938)^Age

Where κ is 0.7 for females and 0.9 for males, and α is -0.241 (females, Scr ≤ κ) or -1.200 (females, Scr > κ), with corresponding values for males. Your laboratory software runs this automatically. You never need to calculate it by hand. What you do need is to understand what the number means clinically.

Why Creatinine Has Limits

Creatinine is a byproduct of muscle metabolism. Bodybuilders and people eating high-protein diets produce more creatinine, which can make eGFR appear lower than true GFR. Conversely, elderly patients with low muscle mass may have a falsely reassuring eGFR. When creatinine-based eGFR is ambiguous, clinicians add cystatin C, a protein produced at a constant rate regardless of muscle mass. The 2021 CKD-EPI Creatinine-Cystatin C equation improves accuracy and is recommended by KDIGO when confirmation matters (2).

The Five CKD Stages and What Each Number Means

The Kidney Disease: Improving Global Outcomes (KDIGO) 2024 Clinical Practice Guideline classifies kidney function into five G-stages based on eGFR (3):

| Stage | eGFR (mL/min/1.73 m²) | Description | |---|---|---| | G1 | ≥90 | Normal or high; kidney damage present if albuminuria or imaging abnormality exists | | G2 | 60 to 89 | Mildly decreased | | G3a | 45 to 59 | Mildly to moderately decreased | | G3b | 30 to 44 | Moderately to severely decreased | | G4 | 15 to 29 | Severely decreased | | G5 | <15 | Kidney failure |

Stage G1 or G2 alone does not diagnose CKD. Kidney damage (albuminuria, structural abnormality, or pathologic finding) must also be present. An isolated eGFR of 65 with no proteinuria and a normal kidney ultrasound is not CKD by KDIGO criteria.

The 90-Day Rule

A single low eGFR reading does not diagnose CKD. You need two readings below the threshold, separated by at least 90 days, to confirm chronicity. Acute kidney injury (AKI) from dehydration, NSAIDs, or contrast dye can temporarily drop eGFR into Stage G3 or lower and then recover fully. Retesting prevents unnecessary anxiety and overdiagnosis.

Albuminuria as a Co-Classifier

KDIGO pairs eGFR with albuminuria categories (A1: <30 mg/g; A2: 30 to 300 mg/g; A3: >300 mg/g) to create a risk grid. A patient with eGFR 55 (G3a) and microalbuminuria (A2) carries moderately high risk of CKD progression. The same eGFR with A1 albuminuria carries low risk. Always read eGFR alongside your urine albumin-to-creatinine ratio (UACR) for a full picture.

Normal eGFR Ranges by Age

EGFR naturally declines with age. Average measured GFR in healthy 20-to-29-year-olds is approximately 116 mL/min/1.73 m², dropping to roughly 75 mL/min/1.73 m² by age 70, according to data from the CKD-EPI development cohort (4). This means an eGFR of 68 in a 72-year-old with no proteinuria and normal kidneys on imaging may reflect physiologic aging rather than CKD.

Age-stratified approximate averages for healthy adults:

| Age Range | Approximate Mean eGFR | |---|---| | 20 to 29 | 116 | | 30 to 39 | 107 | | 40 to 49 | 99 | | 50 to 59 | 93 | | 60 to 69 | 85 | | 70+ | 75 |

These figures come from healthy reference populations. Your result should be interpreted in context of your specific age, clinical history, and UACR.

When a "Normal" Number Still Warrants Concern

Trending matters as much as any single value. Losing more than 5 mL/min/1.73 m² per year, or more than 10 mL/min/1.73 m² over two years, is considered a rapid decline and warrants nephrology referral even if the absolute eGFR remains above 60 (3). A patient dropping from 90 to 72 over 18 months is more concerning than one stable at 58 for five years.

What a Low eGFR Means Clinically

Causes of Reduced eGFR

The two most common causes of chronically low eGFR are diabetic kidney disease and hypertensive nephropathy, together accounting for roughly 75% of U.S. End-stage renal disease cases according to the United States Renal Data System (5). Other causes include glomerulonephritis, polycystic kidney disease, lupus nephritis, and obstructive uropathy.

Reversible causes of acutely low eGFR include:

• Volume depletion (vomiting, diarrhea, diuretics)
• NSAID use (constricts afferent arterioles)
• ACE inhibitors or ARBs in the setting of bilateral renal artery stenosis
• Contrast-induced nephropathy
• Rhabdomyolysis

Symptoms You May or May Not Have

Most people with eGFR between 30 and 60 have no symptoms at all. That is precisely why routine laboratory screening catches it. Fatigue, fluid retention, decreased urine output, nausea, and difficulty concentrating typically appear at eGFR below 15 to 20. The ADA's 2024 Standards of Care recommend annual UACR and eGFR for all patients with type 2 diabetes, starting at diagnosis, because early CKD is silent (6).

Cardiovascular Implications

Low eGFR is an independent cardiovascular risk factor. The SHARP trial (N=9,438) showed that patients with CKD Stages G3, G5 had a 17% relative risk reduction in major atherosclerotic events with simvastatin plus ezetimibe versus placebo (7). Cardiorenal risk management therefore requires addressing lipids, blood pressure, and proteinuria simultaneously, not just tracking eGFR alone.

What a High eGFR Means

An eGFR above 90 with no kidney damage markers is simply normal. Values above 120 mL/min/1.73 m² may reflect hyperfiltration. Diabetic hyperfiltration, where early-stage diabetes increases GFR above baseline, can temporarily read as 130 or higher. This can mask early kidney injury by making the kidneys appear overperforming. Over time, hyperfiltration damages glomeruli, and eGFR eventually falls. An eGFR consistently above 120 in a person with diabetes or obesity is worth monitoring, not celebrating.

Pregnancy also raises true GFR by 40 to 60% due to increased cardiac output and renal plasma flow. A pregnant patient with an eGFR of 130 is normal for gestation. Standard CKD-EPI equations are not validated in pregnancy; clinicians use clinical judgment and 24-hour urine collection when needed.

eGFR and Medication Dosing: The Clinical Decisions That Depend on Your Number

This is where eGFR becomes directly actionable for people on common telehealth medications.

Metformin

The FDA label and the ADA 2024 Standards of Care (6) state:

• eGFR ≥45: metformin is safe, no dose adjustment required
• eGFR 30 to 44: metformin may be continued with caution and more frequent monitoring
• eGFR <30: metformin is contraindicated due to lactic acidosis risk

The concern is not direct kidney toxicity. Metformin accumulates when the kidneys cannot clear it fast enough, raising plasma lactate. Stopping metformin before contrast procedures when eGFR is 30 to 60 is still standard practice at most institutions.

GLP-1 Receptor Agonists

Semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound) do not require dose adjustment based on eGFR down to approximately 15 mL/min/1.73 m², according to their FDA prescribing information (8). In fact, the FLOW trial (N=3,533) demonstrated that semaglutide 1.0 mg weekly reduced the risk of a major kidney disease event by 24% compared to placebo in patients with CKD and type 2 diabetes (hazard ratio 0.76, 95% CI 0.66 to 0.88, P<0.001), establishing a direct renoprotective signal (9).

The AACE/ACE 2023 Comprehensive Diabetes Management Algorithm states: "GLP-1 receptor agonists are preferred in patients with CKD because of their cardiorenal protective effects and low hypoglycemia risk" (10).

SGLT2 Inhibitors

Empagliflozin, dapagliflozin, and canagliflozin require eGFR above specific thresholds to exert glycemic benefit (typically eGFR ≥30 or ≥45 depending on the agent), but their kidney-protective effects, demonstrated in CREDENCE (N=4,401) and DAPA-CKD (N=4,304), extend to patients with eGFR as low as 25 mL/min/1.73 m² (11) (12).

Testosterone Replacement Therapy (TRT)

Testosterone itself does not require eGFR-based dose adjustment, but erythrocytosis (elevated hematocrit from TRT) increases blood viscosity and can worsen renal perfusion in patients with already-reduced eGFR. Monitoring hematocrit and eGFR at the same interval, typically every 6 to 12 months, is reasonable clinical practice.

NSAIDs and Contrast Agents

Patients with eGFR below 60 should avoid regular NSAID use. The risk of acute-on-chronic kidney injury is substantially higher in Stage G3 and below. Gadolinium-based contrast agents are generally safe down to eGFR 30; iodinated contrast for CT requires risk-benefit discussion below eGFR 45.

How to Raise a Low eGFR (and What Can and Cannot Be Changed)

The following decision framework reflects current KDIGO 2024 and ADA 2024 guidance. It is intended as a clinical reference tool, not a substitute for individualized physician assessment.

Modifiable Factors That May Slow Decline

1. Blood pressure control. Target below 120/80 mmHg in most CKD patients per the SPRINT trial findings, though individualization is required. RAAS blockade with an ACE inhibitor or ARB reduces intraglomerular pressure and proteinuria regardless of systemic blood pressure (13).

2. Proteinuria reduction. Every 50% reduction in UACR is associated with a roughly 30% lower risk of CKD progression. Finerenone (a non-steroidal MRA) reduced a composite kidney endpoint by 18% in FIGARO-DKD (N=7,437) in patients with diabetic CKD (14).

3. Blood glucose management. A1C targets around 7.0% slow diabetic nephropathy progression based on DCCT/EDIC long-term follow-up data (15).

4. Protein intake. Dietary protein restriction to 0.6 to 0.8 g/kg/day may slow progression in non-dialysis CKD, though evidence is moderate-quality per a 2020 Cochrane Review (16).

5. Weight loss. Obesity-related hyperfiltration can be partially reversed with weight loss. The LOOK AHEAD trial found sustained weight loss of 8 to 10% reduced incident CKD progression in overweight adults with type 2 diabetes over 10 years (17).

6. Smoking cessation. Smoking accelerates CKD progression independently of hypertension and diabetes. Quitting may reduce the rate of eGFR decline by 2 to 5 mL/min/1.73 m² per year in heavy smokers.

What Will Not Meaningfully Raise eGFR

Supplements marketed as "kidney cleansers," including astragalus, baking soda loading (outside of formal bicarbonate supplementation in metabolic acidosis), and high-dose vitamin C, lack rigorous trial evidence supporting eGFR improvement. Bicarbonate supplementation (1.0 to 1.5 g twice daily) is evidence-supported specifically for CKD patients with serum bicarbonate below 22 mEq/L to slow progression, not for patients with normal acid-base status (3).

Creatine supplementation raises serum creatinine without affecting true GFR. This artificially lowers the calculated eGFR and can cause unnecessary alarm. Stopping creatine for two weeks before a kidney function panel gives a more accurate reading.

When to Refer to Nephrology

The KDIGO 2024 guideline recommends nephrology referral for (3):

• eGFR <30 (G4 or G5)
• Rapid decline: loss of ≥5 mL/min/1.73 m² per year
• UACR above 300 mg/g (severely increased albuminuria)
• Unexplained hematuria with proteinuria
• Refractory hypertension despite three antihypertensives
• Suspected non-diabetic kidney disease

Primary care clinicians and telehealth providers manage the majority of G1, G3a CKD. G3b and above, or any case with rapid decline, benefit from co-management with nephrology.

How eGFR Is Reported and What to Check on Your Lab Result

Most U.S. Labs now report eGFR calculated with the 2021 CKD-EPI Creatinine equation. Some older labs still use MDRD. If your report says "MDRD GFR," the number is less accurate, particularly above 60 (MDRD is known to underestimate GFR at higher values). Ask your provider to run the CKD-EPI 2021 equation, or request cystatin C-based eGFR if muscle mass is a confounding factor.

Your report may say "eGFR >60" or "eGFR >90" rather than a precise number. Labs often cap their reporting at 60 or 90 because the CKD-EPI equation's precision above 60 is lower than below it. A result of ">60" is reassuring, but does not tell you whether you are at 62 or 105. If you are tracking trends over time, request the uncapped numeric value.

Summary Table: Key eGFR Thresholds and Clinical Actions

| eGFR (mL/min/1.73 m²) | Clinical Stage | Key Actions | |---|---|---| | ≥90 | G1 (if damage present) or normal | Annual monitoring if diabetes/HTN present | | 60 to 89 | G2 or age-normal | Monitor UACR; address risk factors | | 45 to 59 | G3a CKD | Intensify BP and glucose control; review all medications | | 30 to 44 | G3b CKD | Stop metformin if <30 approaching; nephrology co-management | | 15 to 29 | G4 CKD | Nephrology referral; prepare for renal replacement options | | <15 | G5 / Kidney Failure | Dialysis or transplant evaluation |