You go in for your annual physical. You feel fine. Your doctor orders some blood work, and a few days later the results pop up in your patient portal.
Creatinine: 1.2
eGFR: 64
Then you see something called BUN, perhaps a BUN/creatinine ratio, and maybe a urine test for albumin.
And if you are like many people, your first thought is:
Are my kidneys okay?
After nearly four decades of practicing internal medicine, I can tell you that kidney test results cause a lot of unnecessary confusion. Part of the problem is that we don’t have one simple test that says:
Kidney function: 87%. Everything looks good.
Instead, we use several different tests that give us clues about how well your kidneys are working and whether they may be getting damaged.
Let’s make those numbers a little less mysterious.
First, What Are Your Kidneys Actually Doing?
Most people know that the kidneys make urine. But that’s only part of the job.
Your kidneys are remarkable little organs. Every day they continuously filter your blood, removing waste products and excess water.
They also help:
- Balance sodium, potassium, and other minerals
- Regulate the amount of fluid in your body
- Control blood pressure
- Maintain your body’s acid-base balance
- Stimulate red blood cell production
- Keep your bones healthy
Think of your kidneys as a combination filtering system, chemistry laboratory, and fluid-management department.
When we test your kidneys, we’re trying to determine how well those jobs are being performed.
Creatinine: The Number Most People See
Creatinine is a waste product produced primarily from normal muscle metabolism. Your muscles produce it continuously. It enters your bloodstream, and your kidneys remove most of it.
That makes creatinine useful. If your kidneys aren’t filtering blood as efficiently, creatinine can accumulate in your bloodstream.
In general:
Higher creatinine can mean poorer kidney filtration.
But—and this is important—creatinine isn’t a perfect kidney test.
Someone with a lot of muscle may naturally have a higher creatinine. Someone who is older, frail, or has very little muscle may have a relatively low creatinine even when kidney function isn’t ideal.
Dehydration, certain medications, supplements, recent intense exercise, and other factors can sometimes influence the result as well.
Dr. Mike’s Take
Don’t judge your kidneys by the creatinine number alone.
It is one piece of the puzzle. Your doctor will usually interpret it along with your eGFR, urine testing, previous results, medications, medical history, and other factors.
eGFR: Your Estimated Filtering Ability
The next number you are likely to see is eGFR, which stands for:
Estimated Glomerular Filtration Rate.
That’s quite a mouthful. You can think of it as an estimate of how effectively your kidneys are filtering your blood.
The calculation generally uses your blood creatinine along with factors such as your age and sex.
As kidney filtration decreases, the eGFR generally decreases.
A simplified way to think about it is:
- 90 or higher: generally normal or high filtration
- 60–89: mildly decreased filtration
- 45–59: mild-to-moderate decrease
- 30–44: moderate-to-severe decrease
- 15–29: severe decrease
- Below 15: kidney failure range
But here’s where people sometimes get frightened unnecessarily.
One eGFR of 58 does not automatically mean you have chronic kidney disease.
Chronic kidney disease generally requires abnormalities of kidney structure or function that persist for at least three months and have implications for your health.
Your doctor is interested in the trend.
Was your eGFR 82 five years ago, 70 last year, and 58 today?
That’s different from someone whose eGFR has remained around 60 for years.
Remember This
Kidney numbers are often more useful as a movie than as a photograph.
The trend over time can tell us much more than one isolated laboratory result.
Urine Albumin: The Test Too Many People Don’t Know About
If I could get you to remember one additional kidney test, it would be this one.
Healthy kidneys are very good at keeping important proteins in your bloodstream.
When the kidney’s filtering units become damaged, however, small amounts of a protein called albumin may begin leaking into the urine.
We can measure this with a urine albumin-to-creatinine ratio, often abbreviated UACR or ACR.
In general:
- Below 30 mg/g: normal to mildly increased
- 30–300 mg/g: moderately increased
- Above 300 mg/g: severely increased
Why does this matter?
Because you can have kidney damage even when your eGFR still looks pretty good.
This is particularly important for people with diabetes or high blood pressure—two of the most common causes of chronic kidney disease.
Albumin in the urine can sometimes be temporary, however. Exercise, illness, fever, urinary infections, and other factors can affect the result. An abnormal test may therefore need to be repeated.
The Bottom Line
eGFR tells us how well the kidneys are filtering.
Urine albumin helps tell us whether the kidney filters are being damaged.
We want to know both.
What About BUN?
Another common number on your blood work is BUN, or blood urea nitrogen.
Urea is a waste product created when your body breaks down protein. Your kidneys help remove it.
A high BUN can occur when kidney function declines.
But BUN is influenced by many other things.
For example, it can increase with:
- Dehydration
- A high-protein diet
- Certain medications
- Gastrointestinal bleeding
- Some illnesses
That’s why I would never look at a mildly elevated BUN by itself and declare that someone has kidney disease.
It needs context.
What About Potassium?
Potassium isn’t technically a test of kidney filtration, but it tells us something important about one of the kidneys’ major responsibilities.
Your kidneys help keep potassium within a relatively narrow range.
When kidney function becomes significantly impaired, potassium can sometimes rise.
That’s important because potassium helps regulate the electrical activity of your heart.
Too high—or too low—can potentially become dangerous.
Your doctor may therefore pay close attention to potassium if you have kidney disease or take medications that affect kidney function or potassium levels.
Your Urinalysis Can Tell Us Even More
The humble urine test can provide a surprising amount of information.
A routine urinalysis may look for:
- Protein
- Blood
- Glucose
- White blood cells
- Signs of infection
- Abnormal cells or casts
- Urine concentration
Blood or protein in the urine doesn’t automatically mean kidney disease, but it may be a clue that deserves further evaluation.
Sometimes the urine tells us something the blood tests haven’t revealed yet.
Don’t Panic Over One Abnormal Number
This may be the most important message in this article.
Laboratory reference ranges make medicine look much more black-and-white than it really is.
Your result is either highlighted or it isn’t.
Unfortunately, your body doesn’t know that.
A slightly abnormal kidney test could be related to dehydration, medications, recent illness, exercise, muscle mass, or normal laboratory variation.
That’s why doctors often repeat an unexpected result before drawing conclusions.
What matters is the whole picture.
When Should You Pay More Attention?
I would be particularly interested if:
- Your eGFR is steadily declining
- Your eGFR remains below 60
- Albumin repeatedly appears in your urine
- There is unexplained blood in your urine
- Your creatinine is rising
- Your potassium becomes abnormal
- You have diabetes or high blood pressure and haven’t had appropriate kidney screening
The earlier kidney problems are identified, the more opportunity we have to address the things that may be contributing to them.
And remember: early chronic kidney disease frequently causes no symptoms at all.
You can feel perfectly fine.
That’s why testing matters.
Dr. Mike’s Prescription
The next time you have routine blood work, don’t just look to see whether your kidney tests are marked H or L.
Know these three numbers:
1. Creatinine
A waste product that helps us estimate kidney filtration.
2. eGFR
An estimate of how effectively your kidneys are filtering your blood.
3. Urine albumin-to-creatinine ratio (UACR)
A test that can reveal early damage to the kidney’s filters.
And most importantly, look at how those numbers are changing over time.
If you have diabetes, high blood pressure, heart disease, or another condition that increases your risk of kidney disease, ask your healthcare professional whether your kidney screening is up to date.
You don’t need to become your own nephrologist.
But understanding a few numbers can help you ask better questions and take better care of two organs that quietly work for you 24 hours a day, seven days a week.
That’s a pretty good reason to keep an eye on them.
Quick Takeaway
If you remember only three things:
eGFR = How well are my kidneys filtering?
Urine albumin = Are my kidney filters leaking protein?
Trend = Are things stable, improving, or getting worse?
One abnormal number isn’t necessarily a diagnosis.
But a pattern deserves attention.