You know how it is – you’ve had your routine blood tests, and now you’re looking at the report. So many numbers and abbreviations! One you might see is “eGFR.” It might not be as familiar as, say, cholesterol, but it’s a really important one for us to keep an eye on, especially when it comes to your kidney health. An eGFR, or estimated glomerular filtration rate, gives us a good idea of how well your kidneys are doing their job.
So, What Exactly is eGFR?
Alright, let’s break this down. Inside your kidneys, you have millions of tiny filters called glomeruli. Think of them like microscopic sieves. Their main task? To clean your blood by removing waste products and extra water, which then become urine.
The eGFR is our best estimate of how much blood these little filters are cleaning each minute, adjusted for your body size. It’s not a direct measurement – that’s a super complex process usually reserved for research – but a very helpful calculation we get from a common blood test.
This number is a big help for us doctors. It helps us spot early signs of kidney trouble, sometimes long before you’d ever feel anything is wrong. You see, kidney disease can be a bit sneaky. Symptoms like urinating more often or muscle cramps might not show up until your kidneys have lost a fair bit of their function. The eGFR helps us catch things earlier, which is always better.
Who Should Pay Attention to Their eGFR?
We often check eGFR as part of routine blood work. But we pay extra close attention if you have certain conditions that might put your kidneys at higher risk. Things like:
- Diabetes
- High blood pressure
- A family history of kidney disease
- Heart disease
- Frequent urinary tract infections (UTIs) or blockages
- Obesity
- If you’re taking certain medications long-term
- Sometimes, if there were kidney issues right from birth
Monitoring eGFR in these situations helps us track your kidney health over time and see if chronic kidney disease might be developing or progressing.
How Do We Figure Out Your eGFR?
As I mentioned, it’s an estimated rate. We get it using a formula. This formula takes the result from a serum creatinine blood test and combines it with a few bits of information about you:
- Your age
- Your sex
- Your height and weight
- Sometimes, race or ethnicity is factored in (more on that in a moment)
Now, about creatinine. It’s a waste product. Your body makes a substance called creatine to give your muscles energy. When your muscles use that energy, creatinine is produced. Healthy kidneys filter this creatinine out of your blood, and you pee it out. If your kidneys aren’t working so well, creatinine can build up in your blood. So, a higher creatinine level often means the kidneys aren’t filtering as efficiently.
Preparing for the Creatinine Test
The serum creatinine test is pretty sensitive. I’ll always give you specific instructions, but generally:
- You might need to fast (no food, just liquids) for a bit before the test.
- We might ask you to hold off on certain medications.
- Sometimes, we advise not eating cooked meat the day before, as it can temporarily nudge creatinine levels up.
Understanding Your eGFR Results
Okay, so you’ve got your eGFR number. What does it mean? We measure it in milliliters per minute per body surface area (mL/min/1.73m² – a bit of a mouthful, I know!).
- Generally, an eGFR higher than 60 mL/min/1.73m² suggests your kidneys are working reasonably well. The higher the number, usually the better.
- It’s normal for eGFR to gradually decline a bit as we age, just like other body functions might slow down. For example, someone in their 20s might have an eGFR around 116, while for someone in their 60s, it might be closer to 85. This is quite typical.
A Note on Different eGFR Numbers
You might notice your lab report sometimes shows two eGFR values: one for individuals identified as Black and one for non-Black individuals. This is because, historically, calculations have included race based on observations that, on average, people of African ancestry may have higher muscle mass and thus produce more creatinine. The lab doesn’t know your specific background, so sometimes both are provided. It’s an area of ongoing discussion in medicine, and we’re always looking to refine these tools to be as accurate for everyone as possible. We’ll discuss what number is most relevant for you.
eGFR and Kidney Disease Stages
If your eGFR stays below 60 for three months or more, we start thinking about chronic kidney disease (CKD). CKD is staged based on the eGFR:
- Stage 1: eGFR of 90 or higher. This means there might be early signs of kidney damage (like protein in the urine), but kidney function is still good.
- Stage 2: eGFR between 60 and 89. Mildly reduced kidney function, with some signs of kidney damage.
- Stage 3: eGFR between 30 and 59. Moderately reduced kidney function. This is often when symptoms might start to appear. Stage 3 is sometimes split into 3a (45-59) and 3b (30-44).
- Stage 4: eGFR between 15 and 29. Severely reduced kidney function.
- Stage 5: eGFR below 15. This is kidney failure. At this point, the kidneys are doing very little of their job, and treatments like dialysis (using a machine to clean your blood) or a kidney transplant are needed.
What if My eGFR is Low?
If your eGFR comes back lower than we’d like, please don’t panic. One test result is just a snapshot. We’ll likely want to repeat it and may suggest a few other checks to get a fuller picture. These might include:
- Urinalysis: We’ll check your urine for things like protein (called albumin) or blood, which can be early signs of kidney issues.
- Kidney ultrasound or CT scan: These imaging tests let us look at the structure of your kidneys and check for things like kidney stones or blockages.
- Creatinine clearance test: This compares creatinine in your urine and blood over a 24-hour period.
- Kidney biopsy: In some cases, if we need more specific information about what’s causing kidney damage, a tiny sample of kidney tissue is taken and looked at under a microscope by a specialist called a pathologist.
We’ll always discuss what these tests mean and what the next steps might be for you.
Take-Home Message: Understanding Your eGFR
Here’s what I really want you to remember about eGFR:
- It’s an estimate of how well your kidneys are filtering waste from your blood.
- It’s calculated from a serum creatinine blood test, along with factors like your age and sex.
- An eGFR above 60 is generally good; below 60 for a few months might indicate chronic kidney disease.
- Knowing your eGFR helps us detect kidney problems early, often before symptoms appear.
- If your eGFR is low, we have ways to investigate further and plan how to best protect your kidney health.
When to Reach Out
If you already know you have kidney disease, or if you have risk factors we’ve talked about, give me a call if you notice any new or worsening symptoms like:
- Urinating much more or much less, or seeing blood in your urine or foamy urine.
- Really dry, itchy skin.
- Feeling incredibly tired all the time (fatigue).
- Muscle spasms or cramps.
- Feeling sick to your stomach (nausea) or vomiting.
- Shortness of breath.
- Swelling in your hands, feet, or ankles.
Remember, we’re partners in your health. Understanding these tests is a part of that. You’re not alone in figuring this out.
