Most people don’t think about their kidneys until something goes wrong. But by the time symptoms like swelling, fatigue, or foamy urine show up, up to 50% of kidney function may already be gone. That’s why simple blood and urine tests-creatinine, GFR, and urinalysis-are some of the most important tools doctors use to catch kidney problems early. These aren’t fancy scans or invasive procedures. They’re basic, affordable, and incredibly powerful if you know what they’re telling you.
What Creatinine Tells You About Your Kidneys
Creatinine is a waste product your muscles make every day as they break down energy. Healthy kidneys filter it out of your blood and flush it out in your urine. When your kidneys start to slow down, creatinine builds up in your bloodstream. That’s why doctors check your serum creatinine level-it’s a simple blood test that gives a quick snapshot of how well your kidneys are filtering.
But here’s the catch: creatinine doesn’t rise until your kidneys have lost a lot of function. About half of your kidney filtering power can be gone before your creatinine level even starts to climb. That’s why relying on creatinine alone can be misleading. A normal creatinine level doesn’t mean your kidneys are healthy-it just means they haven’t failed yet.
Other things can affect creatinine too. If you’re very muscular, your levels might naturally be higher. If you’re older, frail, or have less muscle mass, your creatinine might be lower-even if your kidneys aren’t working well. That’s why creatinine is never used alone. It’s the starting point, not the finish line.
Understanding GFR: The Real Measure of Kidney Performance
That’s where eGFR comes in. Estimated Glomerular Filtration Rate (eGFR) takes your creatinine level and adjusts it for your age, sex, and sometimes ethnicity to give a much better picture of how well your kidneys are actually filtering blood. Think of it like turning a raw number into a score. The higher the eGFR, the better your kidneys are working.
eGFR is measured in milliliters per minute per 1.73 square meters of body surface area. Here’s what the numbers mean:
- 90 or above: Normal kidney function
- 60-89: Mildly reduced function
- 45-59: Mild to moderate decline
- 30-44: Moderate to severe decline
- 15-29: Severe decline
- Below 15: Kidney failure (dialysis or transplant needed)
The equation used to calculate eGFR in the UK and most of the world is called CKD-EPI. It replaced the older MDRD formula because it’s more accurate, especially for people with near-normal kidney function. Most labs now report your eGFR automatically when they run your creatinine test. You don’t have to do the math-your doctor does.
But eGFR isn’t perfect. It can be inaccurate if you’re pregnant, very overweight, under 18, or extremely muscular. In those cases, doctors might use cystatin C, another blood marker that’s less affected by muscle mass. It’s not used as often because it’s more expensive, but it’s a useful backup when creatinine doesn’t tell the full story.
Why Urinalysis Is Just as Important as Blood Tests
Here’s something many people don’t know: you can have normal creatinine and normal eGFR-and still have early kidney damage. How? Because the first sign of kidney disease isn’t always a drop in filtering power. It’s a leak.
Your kidneys normally keep protein, especially albumin, inside your blood. But when the filters are damaged-often from diabetes or high blood pressure-protein starts to slip into your urine. This is called proteinuria, and it’s one of the earliest warning signs of kidney disease.
That’s why urinalysis isn’t just a quick dipstick test anymore. The UK Kidney Association says reagent strips (those colorful paper strips you see in old TV shows) are no longer reliable for screening. Instead, doctors use the Albumin-to-Creatinine Ratio (ACR), which measures how much albumin is in your urine compared to creatinine. It’s more accurate, easier to do than a 24-hour collection, and can be done on a single early-morning urine sample.
Here’s what ACR levels mean:
- Below 3 mg/mmol: Normal
- 3-70 mg/mmol: Microalbuminuria (early kidney damage)
- Above 70 mg/mmol: Macroalbuminuria (more advanced damage)
If your ACR is between 3 and 70, your doctor will likely ask you to repeat the test in a few weeks. One high result could be from dehydration, infection, or intense exercise. Two or three high results over time confirm a problem.
Who Needs These Tests-and How Often?
You don’t need to be sick to get tested. If you’re at risk, you should be screened regularly. That includes people with:
- Diabetes (type 1 or type 2)
- High blood pressure
- Heart disease
- A family history of kidney failure
- Previous acute kidney injury
- Obesity
For most people with diabetes or high blood pressure, the UK Kidney Association recommends checking eGFR and ACR at least once a year. If your numbers are normal, you might only need testing every 2-3 years. If they’re borderline or worsening, your doctor might check every 3-6 months.
Even if you don’t have any risk factors, getting a basic metabolic panel-which includes creatinine and eGFR-once a year during your annual check-up is a smart move. It’s cheap, quick, and could catch a problem before it becomes serious.
What Happens If Your Results Are Abnormal?
An abnormal result doesn’t mean you have kidney failure. It means your kidneys are sending a signal that something needs attention. The next steps depend on your numbers and your health history.
If your eGFR is low but your ACR is normal, your doctor might look for other causes-like dehydration, medications, or blockages. If your ACR is high but your eGFR is normal, that’s early kidney damage. The treatment? Often, it’s simple: better blood pressure control, tighter blood sugar management (if you’re diabetic), and avoiding NSAIDs like ibuprofen. Sometimes, a doctor will prescribe an ACE inhibitor or ARB, medications that not only lower blood pressure but also protect the kidneys by reducing protein leakage.
What you do next matters more than the numbers. Losing 5-10% of your body weight if you’re overweight, cutting back on salt, quitting smoking, and staying active can slow or even stop kidney damage in its tracks. Many people with early-stage kidney disease never progress to dialysis if they act early.
What About 24-Hour Urine Tests?
You might hear about collecting your urine for 24 hours. That test measures total protein, sodium, potassium, and other substances over a full day. It’s more accurate for measuring total protein loss, but it’s also a pain. You have to collect every drop in a special container, keep it cold, and bring it to the lab. Most doctors don’t order it unless they’re trying to diagnose rare conditions like nephrotic syndrome or kidney stones.
For routine monitoring, ACR is the gold standard. It’s easier, cheaper, and just as effective for catching early damage.
Can You Improve Your Kidney Numbers?
Yes. And the sooner you act, the better your chances.
High blood pressure and diabetes are the top two causes of kidney damage. Controlling them is the single most effective thing you can do. That means:
- Keeping blood pressure under 130/80 mmHg
- Keeping HbA1c under 7% if you have diabetes
- Avoiding NSAIDs (ibuprofen, naproxen) unless your doctor says it’s safe
- Drinking enough water (but not overdoing it)
- Not smoking
- Eating less processed food and salt
There’s no magic supplement or diet that fixes kidney disease. But a balanced diet rich in vegetables, lean proteins, and whole grains-like the DASH diet-has been shown to help. And losing weight? That alone can improve eGFR and reduce protein in the urine.
Many people think kidney disease is inevitable if you have diabetes or high blood pressure. It’s not. With early detection and smart lifestyle changes, you can protect your kidneys for decades.
What does a high creatinine level mean?
A high creatinine level usually means your kidneys aren’t filtering waste as well as they should. But it’s not always a sign of disease-muscle mass, age, and dehydration can affect it. Doctors always look at creatinine along with eGFR and urinalysis to get the full picture.
Can I check my kidney function at home?
There are no reliable home tests for eGFR or ACR. Urine dipsticks sold online aren’t accurate enough for early detection. The only way to get trustworthy results is through a blood test and a lab-processed urine sample ordered by your doctor.
Is a low eGFR always serious?
Not always. A single low eGFR result can be caused by dehydration, recent illness, or certain medications. If your eGFR is below 60 for three months or more, that’s when it’s considered chronic kidney disease. Your doctor will look at trends over time, not just one number.
Why is protein in the urine a big deal?
Protein in the urine means the filters in your kidneys are damaged. Even if your eGFR is normal, this is often the earliest sign of kidney disease-especially from diabetes or high blood pressure. Catching it early lets you protect your kidneys before permanent damage happens.
Should I get tested if I feel fine?
Yes-if you have diabetes, high blood pressure, heart disease, or a family history of kidney failure. Kidney disease often has no symptoms until it’s advanced. A simple blood and urine test can catch it early, when treatment works best.
Sarah McQuillan
December 19, 2025 AT 06:13Look, I get that doctors love their fancy eGFR numbers, but in my experience, the real test is whether you can climb a flight of stairs without feeling like you’ve run a marathon. I’ve seen people with ‘normal’ creatinine dropping like flies because no one looked at their actual symptoms. Lab values don’t feel fatigue. Your body does.
anthony funes gomez
December 20, 2025 AT 09:00It's worth noting, of course, that the CKD-EPI equation-while statistically superior to MDRD in cohort studies-still relies on assumptions of linear renal clearance, homogenous muscle mass distribution, and demographic homogeneity that simply don't hold in real-world populations, particularly among aging, obese, or ethnically diverse cohorts. The implicit normalization to 1.73 m² BSA is, frankly, a relic of 20th-century anthropometric bias.
pascal pantel
December 21, 2025 AT 19:16Let’s be real-these tests are just a money machine. Labs make bank on creatinine panels. Doctors get paid for follow-ups. Pharma pushes ACE inhibitors like candy. Meanwhile, nobody talks about how glyphosate and PFAS are wrecking kidneys at the population level. You think your ACR is high because of sugar? Nah. It’s because your water’s laced with industrial runoff and your doctor’s too busy to mention it.
Gloria Parraz
December 22, 2025 AT 19:45This is the kind of information that could literally save lives. I’m so glad someone broke this down so clearly. If you have diabetes or high blood pressure-don’t wait for symptoms. Get tested. Even if you feel fine. Your future self will thank you. I wish I’d known this 10 years ago.
Sahil jassy
December 23, 2025 AT 03:21Same here in India. Many people think kidney problems only happen to old folks. But with sugar and salt everywhere, even 30-year-olds are showing early signs. ACR test is cheap here-just 300 rupees. Do it. No excuses.
Kathryn Featherstone
December 24, 2025 AT 19:58I’ve been tracking my eGFR for three years now. It dropped from 88 to 72. My doctor said it’s ‘mildly reduced’ and to come back in a year. But I started cutting out processed food, walking daily, and drinking more water. Six months later, it went back up to 80. It’s not just about meds-it’s daily choices. Small things matter.