What Is eGFR, and What Does a Low Result Mean?

eGFR stands for estimated glomerular filtration rate. It estimates how many milliliters of blood your kidneys filter every minute. It is calculated, not measured directly, from your blood creatinine level together with your age and sex. A low eGFR means the kidneys are filtering more slowly than expected. That may reflect real damage. It may also reflect the day you had the test.

That distinction is the whole point. One low reading is not chronic kidney disease. Most people come looking with a single number from a report, so the number is where we start.

What your exact number means#

The units are mL/min/1.73m2. The 1.73m2 part adjusts the result to an average adult body size, so the figure can be compared between people.

A number on its own is not a diagnosis. Chronic kidney disease means an eGFR below 60 lasting at least three months. It also covers evidence of kidney damage, such as protein in urine, when eGFR is normal. One reading tells you almost nothing about which of those applies.

The numbers people search for most#

113, 123, 100 or 98. All normal. Above 90 is standard filtration, and many labs report anything above 90 simply as normal. A very high figure is not better than a merely normal one.

89 and 80. Both fall in the mildly reduced band, and both are ordinary. An 89 and a 91 are the same kidney either side of a rounding line. With no protein in the urine, neither is kidney disease.

68 and 64. Still mildly reduced, still above the disease threshold, and very common after 50. These usually mean monitoring and a urine test, not treatment.

60. The boundary itself. A single 60 is repeated before anything is concluded. Sixty with a clean urine test in a 70 year old is generally age related.

54. Stage 3a if it persists for three months. Most people feel completely well. It prompts a repeat test, a urine albumin ratio, and a look at blood pressure, blood sugar and medicines.

43. Stage 3b. This needs organized follow up: more frequent blood tests, medicine dose checks, and often a specialist opinion. It is not kidney failure.

21. Stage 4. This level needs a kidney specialist. Care shifts toward protecting what remains and planning ahead calmly.

CKD-EPI and the older MDRD formula#

Two formulas are in common use. The CKD-EPI 2021 equation is the current standard and is more accurate at higher filtration rates. The older abbreviated MDRD equation underestimates eGFR in people with near normal kidneys. Many labs using it report only "greater than 60" rather than an exact figure. So a "low" MDRD result in the 60s may read differently on the newer formula. Our eGFR calculator shows how age, sex and creatinine combine.

eGFR falls with age in everyone#

This is the piece most reports leave out. Filtration peaks in the twenties and then declines slowly, by roughly 0.5 to 1 point per year after 40. A healthy 75 year old often has an eGFR in the 60s or low 70s.

That decline is not a disease. It becomes one when it is faster than expected, or when albumin appears in the urine. Judging a 70 year old against a 25 year old's number produces needless worry and needless tests.

Why the test is done, and who should have it#

eGFR appears on almost every routine blood panel, because creatinine is cheap to measure and the calculation is free. It is usually there for one of four reasons.

• Screening in people at higher risk: diabetes, high blood pressure, heart disease, or a family history of kidney disease.
• Checking whether a medicine is safe at your usual dose, since many drugs are cleared by the kidneys.
• Investigating symptoms such as swelling, frothy urine, or unexplained tiredness.
• Tracking a known reduction over time.

If you have diabetes or high blood pressure, yearly testing of both blood eGFR and urine albumin is standard.

The urine test matters as much as the blood test#

The single most useful companion test is the urine albumin to creatinine ratio, or ACR. Protein leaking into the urine shows damage to the filters themselves. It predicts progression and heart risk better than eGFR alone.

An eGFR of 70 with significant protein in the urine is more worrying than an eGFR of 62 with none. If you have only had the blood test, the urine test is a reasonable thing to ask about. Our guide to microalbuminuria explains what those numbers mean.

What makes the number wrong on a given day#

Creatinine comes from muscle. More muscle means higher creatinine and so a lower calculated eGFR. That is why bodybuilders and heavy manual workers are sometimes flagged incorrectly. Very low muscle mass does the opposite and can hide real impairment in a frail older adult.

Things that lower a single reading without any kidney damage:

• Dehydration, including a hot day or a long shift without fluids.
• A large meat meal in the hours before the blood draw.
• Hard exercise the day before.
• Creatine supplements taken regularly.
• Some medicines, including trimethoprim and certain diabetes drugs, which block creatinine secretion without changing filtration.

Reference creatinine for most adults is roughly 0.6 to 1.2 mg/dL (53 to 106 micromol/L), and small shifts inside that range move eGFR noticeably.

Why an eGFR drops#

A slow drift down with age is expected. A fall of more than about 5 points a year is not, and neither is a sudden drop over weeks.

The usual drivers are blood pressure higher than it looks at home, creeping blood sugar, and regular anti-inflammatory painkillers. Repeated dehydration, untreated sleep apnea, and recurring urine infections add to it. A sudden fall during an illness with vomiting or diarrhea is often acute and reversible, but it needs same week attention.

What a doctor does next#

The sequence is fairly standard. Expect a repeat eGFR after two to twelve weeks, depending on how low the first was. Expect a urine ACR, a urine dipstick for blood, and a check of blood pressure. Blood tests for glucose or HbA1c, calcium, phosphate, potassium and hemoglobin follow if eGFR is below 60.

An ultrasound is common when the cause is unclear, when there is blood in the urine, or when the fall was fast. Referral to a kidney specialist is usual for an eGFR below 30, for heavy protein loss, or for a rapid decline at any level. Our guide on why doctors repeat a blood test explains the logic behind the wait.

What eGFR cannot tell you#

It is an estimate of speed, not a picture of the organ. It cannot tell you the cause of a reduction. It cannot separate long standing damage from a temporary dip. It cannot tell you whether the kidneys are inflamed, blocked, scarred or simply older.

It is also less reliable at the extremes: very muscular people, people with little muscle, pregnancy, limb amputation, and rapidly changing illness. A cystatin C based estimate is sometimes used when the creatinine result does not fit the person.

What protects kidney function#

Diabetes and high blood pressure are the two dominant causes of chronic kidney disease worldwide. Controlling both is the most effective protection there is, and blood pressure control has the strongest evidence of anything on the list.

Beyond that: avoid regular use of anti-inflammatory painkillers such as ibuprofen if your eGFR is already reduced. Stay well hydrated in hot conditions. Stop smoking. Keep salt intake down. Tell every prescriber your eGFR so doses can be adjusted.

During an illness with vomiting or diarrhea, some medicines are temporarily paused. Ask your doctor which of yours are on that list.

What I see most often#

Three patterns repeat.

The first is a healthy person in their sixties frightened by a 68 on a report with no explanation attached. Once the urine is clean and the previous result is found, the conversation takes two minutes.

The second is the opposite. A steady drop from 95 to 78 to 66 over three years gets ignored because every value looked acceptable in isolation. The trend was the finding, not any single number.

The third is the person whose eGFR fell after months of a daily over the counter painkiller. Nobody asked, because nobody counts those as medicines.

At work#

Heat and hydration matter more here than most people expect. Repeated heat strain with poor fluid replacement is linked to kidney injury in outdoor and hot indoor work. Repeated mild dehydration across a season is the risk, not one hot afternoon.

Practical steps: drink to a schedule rather than to thirst, take breaks in shade or cooling, and limit anti-inflammatory painkillers on hot days. Solvent and heavy metal exposure also affects the kidneys, so tell occupational health if your eGFR is falling and your job involves either.

When this needs a doctor#

Book a routine appointment for a first eGFR below 60, or for any eGFR you do not understand. Book one for a value that has fallen more than 5 points since last year.

Ask to be seen promptly for an eGFR below 30, or for frothy urine with swollen ankles. The same applies to a fall that happened over weeks rather than years.

Seek urgent care for passing very little urine or none. Get the same urgent care for new confusion, vomiting, or breathlessness with swelling.

The bottom line#

eGFR is a speed estimate, not a verdict. Above 90 is normal. 60 to 89 is usually age rather than disease. Below 60 counts as chronic kidney disease only when it lasts three months. The trend across several tests and the urine albumin result tell you far more than any single figure. If your number surprised you, the next step is a repeat test and a urine ACR, not worry.