Early kidney disease may cause no obvious symptoms, which is why kidney function is often checked through routine blood and urine tests. GFR, creatinine, BUN, and urine albumin on your lab results are numbers that provide useful clues about how your kidneys are functioning.
What Does GFR Mean in a Blood Test?
GFR stands for glomerular filtration rate. It is an estimate of how much blood your kidneys can filter over a certain amount of time.
Your kidneys contain millions of tiny filtering units called glomeruli. As blood passes through them, waste and excess substances are removed while useful substances remain in the bloodstream.
Because directly measuring GFR is difficult, routine blood tests usually report an estimated GFR, or eGFR. Your eGFR is calculated using your blood creatinine level along with factors such as your age and sex.
In general, a higher eGFR indicates better kidney filtration, while a lower eGFR indicates reduced filtration. But an eGFR number needs context. Your age, previous results, other laboratory findings, and overall health can all affect what the number means.
What do the eGFR numbers mean?
eGFR is generally reported in mL/min/1.73 m². The National Kidney Foundation uses the following broad categories:
| eGFR | What It Generally Indicates |
| 90 or higher | Normal or high |
| 60–89 | Mildly decreased |
| 45–59 | Mildly to moderately decreased |
| 30–44 | Moderately to severely decreased |
| 15–29 | Severely decreased |
| Below 15 | Kidney failure |
These categories are not a diagnosis by themselves. For example, an eGFR between 60 and 89 does not automatically mean that you have chronic kidney disease. The trend over time can be just as important as the number itself.
What Is a Normal GFR for a 70-Year-Old?
If you’re over 65, you may notice that your eGFR is lower than numbers you’ve seen described as “normal” for younger adults. That can be expected.
Kidney filtration tends to decrease as people get older. The National Kidney Foundation reports an average eGFR of approximately 75 mL/min/1.73 m² for adults age 70 and older.
That does not mean 75 is a required or ideal number for everyone who is 70. There is no single eGFR that defines normal kidney function for every older adult.
An eGFR in the 60s or 70s may therefore mean something very different in a healthy older adult than it would in a younger person. Your healthcare team may pay particular attention to whether the number is stable, gradually changing, or dropping more quickly than expected.
An eGFR below 60 that persists for at least three months can be a sign of chronic kidney disease. Evidence of kidney damage, such as albumin in the urine, can also be important even when eGFR is above 60.
Why Does GFR Go Down with Age?
Over time, some of the tiny filtering units in the kidneys are lost, and the remaining ones may not filter blood as efficiently as they once did. As a result, GFR generally declines with age.
That does not mean every decline is harmless.
Conditions that become more common with age, including high blood pressure, diabetes, and cardiovascular disease, can also damage the kidneys. Certain medications and repeated episodes of kidney injury can affect kidney function as well.
The useful question is therefore not simply, “Is my GFR lower than it used to be?”
It is: “Is this level of kidney function expected for me, and is it remaining stable?”
What Does Creatinine Tell You?
Creatinine is a waste product produced by normal muscle activity. Your kidneys normally remove it from your blood and pass it into your urine.
When the kidneys filter less efficiently, creatinine can build up in the blood. That’s why your creatinine result is closely connected to your eGFR.
But creatinine has an important limitation: it is influenced by muscle mass as well as kidney function. Someone with a larger amount of muscle may naturally have more creatinine. Someone who has lost muscle mass with age may produce less.
This matters when looking at creatinine levels in older adults. A creatinine result that falls within your laboratory’s reference range does not necessarily mean that kidney filtration is completely normal. Conversely, a mildly elevated creatinine does not automatically mean kidney disease.
This is one reason eGFR is generally more useful than looking at creatinine alone.
Why Your Previous Creatinine Result Matters
Suppose your creatinine was 0.9 mg/dL last year and is now 1.3 mg/dL. Even if the newer result does not look dramatically abnormal on its own, the change may be meaningful.
On the other hand, a creatinine level that has remained relatively stable over several years may be less concerning than a rapidly changing result.
Your lab report provides a snapshot. Comparing current results with previous results provides the trend.
What Does BUN Mean in a Blood Test?
BUN means blood urea nitrogen.
Urea is produced when your body breaks down protein. Your kidneys normally remove urea from the blood and excrete it in urine.
BUN is therefore another measurement that can provide information about kidney function, but it is affected by considerably more than kidney function alone.
A high BUN can occur with:
- Dehydration
- A high-protein diet
- Gastrointestinal bleeding
- Heart failure
- Reduced kidney function
- Certain medications or other health conditions
This is particularly useful to know if you see a high BUN on your lab report. A high BUN does not automatically mean your kidneys are failing.
For example, someone who has been dehydrated may have an elevated BUN without having chronic kidney disease.
That’s why BUN is usually interpreted alongside creatinine and eGFR rather than treated as a standalone kidney test.
What Is the BUN-to-Creatinine Ratio?
You may see BUN/creatinine ratio listed on your laboratory report. Rather than looking at BUN and creatinine separately, this calculation compares the two values. The relationship can sometimes provide clues about what is contributing to an abnormal result.
For example, dehydration can cause BUN to rise disproportionately compared with creatinine.
The ratio is not a diagnosis, however. A healthcare professional considers it alongside your eGFR, other lab results, medications, hydration status, symptoms, and medical history.
Can You Have Kidney Disease Without Symptoms?
Yes, and this is one of the most important things to understand about kidney health.
Early kidney disease often causes no noticeable symptoms. You may feel completely well while changes are already appearing on blood or urine tests. As kidney function becomes more severely reduced, symptoms can develop. These may include:
- Swelling in the legs, ankles, feet, or around the eyes
- Changes in how often you urinate
- Foamy or unusually bubbly urine
- Blood in the urine
- Fatigue
- Nausea or loss of appetite
- Muscle cramps
- Itching
- Changes in concentration or mental alertness
These symptoms can have many possible causes and do not, by themselves, establish that kidney disease is present. But the absence of symptoms also does not rule kidney disease out.
What Does Albumin in Urine Mean?
A urine test can reveal whether the kidneys are allowing protein to leak into the urine.
Albumin is a protein that normally remains in the bloodstream. Healthy kidney filters keep most albumin out of the urine. When those filters become damaged, albumin can begin to pass into the urine.
A common test is the urine albumin-to-creatinine ratio (uACR). Generally:
- Less than 30 mg/g: normal to mildly increased
- 30 mg/g or higher: increased albumin in the urine
An elevated result may be repeated because temporary factors can affect urine albumin.
The important point is that kidney damage and reduced filtration are not exactly the same thing.
You can have an eGFR above 60 and still have evidence of kidney damage if albumin is persistently elevated in your urine.
Putting Your Kidney Numbers Together
Kidney test results make more sense when you look at them as a group. For example:
- eGFR low + creatinine high: This pattern can indicate reduced kidney filtration.
- eGFR stable + creatinine stable: Stability over time can be reassuring, depending on the actual values and the rest of the clinical picture.
- BUN high + creatinine relatively unchanged: Dehydration, diet, or another factor may be contributing to the BUN elevation.
- eGFR above 60 + urine albumin elevated: Kidney damage may be present even though overall filtration remains relatively preserved.
- eGFR falling over time: A downward trend may deserve closer evaluation than a single mildly low result.
These are examples of how the numbers can relate to one another, not ways to diagnose yourself from a lab report.
What Should You Look for in Your Patient Portal?
When reviewing your results online, don’t focus only on whether a number is marked red or flagged as abnormal. Instead, look for four things:
- The actual number: Find your eGFR, creatinine, BUN, and, if available, urine albumin or uACR.
- The laboratory’s reference range: Reference ranges can vary between laboratories. A result outside the stated range deserves context rather than an automatic conclusion.
- Your previous results: A single result tells you what was happening at one point in time. Previous results can show whether your kidney function has been stable or changing.
- The results together: An isolated BUN elevation means something different from a combination of rising creatinine, falling eGFR, and increasing urine albumin.
When Is a Low GFR More Concerning?
A lower eGFR becomes more significant when it is persistent, progressively declining, or accompanied by other evidence of kidney damage. Your healthcare provider may pay closer attention if:
- Your eGFR remains below 60 for three months or longer
- Your eGFR is declining over time
- Your creatinine is increasing
- Albumin is repeatedly present in your urine
- You have conditions that increase the risk of kidney disease
- You develop symptoms associated with more advanced kidney problems
A sudden change can also be different from a gradual age-related decline. Acute kidney injury, dehydration, illness, or certain medications can cause kidney function to change over a relatively short period.
Take Care
If you were wondering “What does GFR mean in a blood test?”, it’s an estimate of how efficiently your kidneys filter your blood. But your eGFR is only one part of the picture.
Creatinine helps estimate kidney filtration. BUN measures another waste product that can rise for reasons other than kidney disease. Urine albumin can reveal kidney damage that may not yet have significantly reduced your GFR.
For older adults, a lower eGFR can also be part of normal aging. The important issue is not simply whether your number is lower than it was when you were younger, but whether it is appropriate for your age and health and whether it is changing over time.
Understanding these numbers can help you spot patterns in your own health information, recognize when something has changed, and have a more informed conversation about what those changes may mean.