GFR Levels Explained: What Does My GFR Mean?

What GFR is and what the number measures

The glomerular filtration rate, shortened to GFR, describes how much blood your kidneys filter each minute. Inside each kidney, around a million tiny filtering units called glomeruli strain waste products, salts and extra fluid out of the blood while keeping cells and most protein in the circulation. Add up the work of all those units and you get the GFR, expressed in millilitres per minute and standardised to a body surface area of 1.73 square metres, written as mL/min/1.73 m2. Standardising the result in this way lets people of different sizes be compared on the same scale.

In everyday care the GFR on your report is almost always an estimate, written eGFR, calculated from a blood marker such as creatinine rather than measured directly. Direct measurement needs an injected tracer and timed blood or urine samples, so it is reserved for special situations. The estimate is good enough for routine decisions, but it is still an estimate, and later sections of this page explain the situations where it can mislead. If you want to calculate an eGFR from creatinine, age and sex, use our CKD-EPI 2021 eGFR calculator, the older MDRD GFR calculator, or the creatinine clearance (Cockcroft-Gault) calculator that many clinicians still use for drug dosing.

A higher number means more filtration. Young healthy adults usually sit at the top of the scale, and the categories below describe how far a result has fallen from that range. The categories come from KDIGO, the international kidney guideline organisation, whose 2024 clinical practice guideline for the evaluation and management of chronic kidney disease is the reference used throughout this page (KDIGO 2024 CKD guideline, Kidney Int. 2024;105(4S):S117-S314). Two ideas from that guideline matter before you interpret any single number. First, eGFR alone is half the picture and albuminuria, meaning albumin protein leaking into the urine, is the other half. Second, chronic kidney disease is a chronic label: an abnormality only counts as CKD when it has persisted for more than 3 months.

The KDIGO G categories in full

KDIGO divides eGFR into six G categories. The table below is the complete set, and the paragraphs that follow explain each band in turn, including typical monitoring and next steps.

G1, 90 or above, normal or high. This is the range expected in healthy younger adults, and on filtration grounds alone it is reassuring. The crucial qualification is that G1 only counts as chronic kidney disease when there is other evidence of kidney damage, such as albumin in the urine, blood in the urine that comes from the kidneys, or an abnormality on imaging. Without that evidence, a G1 result simply means filtration is normal. Typical care is routine: no kidney specific follow up is needed for the number itself, although people with diabetes, high blood pressure or a strong family history still benefit from periodic blood and urine checks because their risk of future damage is higher.

G2, 60 to 89, mildly decreased. A mildly reduced result is extremely common, particularly in older adults, because GFR declines with age on average. Like G1, G2 only counts as chronic kidney disease with other evidence of kidney damage; a value in the 60s or 70s with a normal urine albumin result and no other abnormality is often simply an age related finding. Monitoring is usually light, often a repeat blood test and urine albumin check about once a year for people with risk factors, alongside the usual attention to blood pressure, blood sugar, weight and smoking. A single G2 result is not a reason for alarm, but a steady downward trend across several results deserves discussion.

G3a, 45 to 59, mildly to moderately decreased. This is the first band where the eGFR alone, if it persists for more than 3 months, meets the filtration criterion for chronic kidney disease. Many people in G3a remain stable for years, especially when urine albumin is in the A1 range, and the overall risk depends heavily on that albumin result. Typical monitoring is regular, often every 6 to 12 months, with checks of blood pressure, potassium, haemoglobin and urine albumin. Next steps include reviewing medicines for doses that need adjusting at lower filtration, avoiding regular anti-inflammatory painkillers where possible, and firm control of diabetes and blood pressure, which are the commonest drivers of further decline.

G3b, 30 to 44, moderately to severely decreased. Filtration in this band is reduced enough that complications become more likely, including anaemia, changes in calcium, phosphate and parathyroid hormone, acid build up in the blood, and a higher risk of cardiovascular disease. Risk of progression is clearly higher than in G3a, particularly when albuminuria is present. Monitoring is closer, commonly every 3 to 6 months, and many people in G3b are shared between primary care and a kidney specialist. Practical steps include a full medication review, vaccination and cardiovascular risk management, dietary advice where a clinician recommends it, and prompt attention to illnesses that cause dehydration, which can push function lower.

G4, 15 to 29, severely decreased. At this level the kidneys filter less than a third of the normal amount, and specialist kidney care is standard. Symptoms such as tiredness, poor appetite, itching, swelling and breathlessness may appear, although some people still feel well. Monitoring is frequent and includes blood tests for potassium, bicarbonate, calcium, phosphate and haemoglobin, because complications need active treatment rather than observation alone. Planning becomes a central part of care: discussing future options such as dialysis, transplantation assessment or conservative care well before they are needed, preparing access if dialysis is chosen, and adjusting or stopping medicines that the kidneys can no longer clear safely.

G5, under 15, kidney failure. This is the lowest band, where filtration alone cannot sustain health for long without support. Care is led by a kidney specialist team, and the conversation focuses on kidney replacement therapy, meaning dialysis or transplantation, or on conservative care focused on symptoms and quality of life when replacement therapy is not the right choice for that person. Monitoring is close and individualised, medicines are reviewed carefully, and diet, fluid intake and potassium often need active management. A G5 result that appears suddenly, rather than as the end of a long decline, may reflect acute kidney injury on top of chronic disease and needs urgent assessment, because acute falls can sometimes be partly reversed.

What a normal GFR is by age

People often ask for one normal number, but the honest answer is a range with context. In KDIGO terms, 90 or above is described as normal or high, and 60 to 89 as mildly decreased. What is usual for a person also shifts across life: GFR declines with age on average, so the same value carries different weight at age 30 than at age 80. A result of 65 in a healthy 78 year old with normal urine testing is a common finding that may never progress, while a result of 65 in a 25 year old is unexpectedly low and deserves a fuller work up. This page deliberately avoids a table of precise per age normal values, because published averages vary by population and method and a false sense of precision helps nobody. Judge a result by the category, the trend over time, the urine albumin result, and the person it belongs to.

Why one low result is not a diagnosis

A single low eGFR is a finding, not a diagnosis, for three reasons. First, the estimate moves around: dehydration, a recent illness, a large meat meal, vigorous exercise, and ordinary laboratory variation can each shift the number by several points from one week to the next. Second, KDIGO defines chronic kidney disease by persistence: the abnormality must be present for more than 3 months before the chronic label applies, precisely so that temporary dips are not mislabelled as lifelong disease. Third, a sudden fall may be acute kidney injury, a short term problem with its own causes and its own staging system, covered by our KDIGO AKI staging calculator, rather than chronic disease at all. The standard response to an unexpected low result is therefore repeat testing, usually within a few weeks and again at around 3 months, together with a urine albumin test and a review of medicines and recent illnesses. Only the pattern across those results tells you whether you are looking at noise, an acute episode, or genuine chronic disease. The BUN to creatinine ratio calculator can add context when dehydration or other causes of a temporary rise in waste products are suspected.

The albuminuria half of staging: A1, A2 and A3

eGFR alone is half the picture and albuminuria is the other half. Albumin is the main protein in blood, and healthy glomeruli keep almost all of it out of the urine. When the filters are damaged, albumin leaks through, and the amount in the urine predicts future kidney decline and cardiovascular risk independently of the eGFR. It is measured with a urine albumin to creatinine ratio, usually called ACR, on a spot urine sample. KDIGO divides ACR into three A categories: A1 is under 30 mg/g, described as normal to mildly increased; A2 is 30 to 300 mg/g, moderately increased and historically called microalbuminuria; and A3 is over 300 mg/g, severely increased and historically called macroalbuminuria.

Combining the G and A categories gives the KDIGO risk grid, sometimes called the heat map, which this interpreter uses when you select an albumin category. The pattern is intuitive once you see it: risk rises as eGFR falls and as albuminuria rises, so a person in G3a with A1 albuminuria sits in a lower risk cell than a person in G3a with A3 albuminuria, and someone in G2 with A3 albuminuria can be at very high risk despite a filtration number that looks almost normal. This is why a urine test is not an optional extra after a low eGFR: without it, the risk estimate is incomplete, and treatment decisions that depend on albuminuria, such as certain blood pressure medicines, cannot be made properly.

When eGFR estimates mislead

Because eGFR is calculated rather than measured, anything that changes the blood marker without changing true filtration can distort it. Acute illness is the commonest trap: during an acute kidney injury the creatinine is still rising or falling, so any single estimate lags behind the real function. Muscle mass extremes distort the result in both directions, since creatinine comes from muscle; a bodybuilder may be told their function is lower than it truly is, while a frail person with very little muscle may be told theirs is better than it truly is. Pregnancy changes blood volume and filtration so much that standard equations do not apply and pregnancy specific interpretation is needed. Amputation reduces muscle mass and therefore creatinine production, so equations can overestimate function after a major limb loss. Diet, creatine supplements, and medicines such as trimethoprim that block creatinine secretion add smaller distortions. When the estimate and the clinical picture disagree, clinicians can order a cystatin C based estimate or, rarely, a directly measured GFR to settle the question.

What to do next, stage by stage, in practical terms

Whatever your band, the first practical steps are the same: confirm the result with repeat testing, get a urine ACR if you have not had one, and take the result to a clinician with your full medication list. From G1 and G2, the emphasis is prevention: keep blood pressure and blood sugar controlled, do not smoke, and repeat testing at the interval your clinician suggests. In G3a and G3b, add an active medication review, ask whether doses need adjusting for your filtration level, avoid regular anti-inflammatory painkillers unless your clinician advises them, and treat intercurrent illnesses early, staying hydrated when you are unwell if your clinician agrees. In G4, expect specialist led planning, treatment of complications such as anaemia and bone disease, and structured discussions about future options. In G5, care is specialist led and focuses on dialysis, transplant assessment or conservative care, symptom control, and close monitoring. At every stage, a falling trend matters more than any single value, so keeping your own dated list of results is genuinely useful.

When to seek care promptly

Most reduced results are handled at a routine appointment, but some situations should not wait. Seek care promptly if a result is very low, especially under 30, and it is new or much lower than your previous values; if your results are falling rapidly from test to test; or if you have symptoms that can accompany failing kidneys, such as marked swelling of the legs or face, breathlessness, severe nausea or vomiting, confusion, extreme tiredness, passing very little urine, or pink or frothy urine. A sudden drop during or after an illness, an infection, or starting a new medicine also deserves same day advice, because acute kidney injury is treated most successfully when it is caught early. If you are in G4 or G5 and develop any of these symptoms, contact your kidney team or urgent care service the same day rather than waiting for your next scheduled review.

Related calculators

For the calculations behind these numbers, see the CKD-EPI 2021 eGFR calculator, the creatinine clearance (Cockcroft-Gault) calculator, the MDRD GFR calculator, the KDIGO AKI staging calculator for acute falls in function, and the BUN to creatinine ratio calculator.

Frequently asked questions

References: KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117-S314. Categories, albuminuria staging and the combined risk grid on this page follow that guideline.