I remember a patient, let’s call her Sarah, who came in a while back. She wasn’t feeling drastically unwell, just… off. More tired than usual, a bit of puffiness around her ankles that she’d noticed. Nothing that screamed emergency, but enough for her to feel something wasn’t quite right. It’s often these subtle cues that prompt us to take a closer look, and in many cases, that includes checking how well the kidneys are doing their job with kidney function tests.
These tests are our window into the health of your kidneys, those amazing bean-shaped organs working tirelessly behind the scenes.
What Are Kidney Function Tests, Really?
So, what are we actually looking at with kidney function tests? Well, they’re usually a combination of urine (yes, peeing in a cup!) and blood tests. Their main job is to see how efficiently your kidneys are working. Think of your kidneys as super-smart filters. They clean your blood, get rid of waste products, and keep your body’s fluids and electrolytes – things like sodium and potassium – in balance. Pretty important stuff, right?
Most of these tests focus on tiny filters within your kidneys called glomeruli. You’ve got millions of them! They’re the real workhorses, sifting out the bad stuff from your blood. The tests measure how well these glomeruli are clearing waste.
Now, I know the idea of tests can make anyone a bit anxious. Blood draws aren’t exactly a walk in the park for everyone, and handing over a urine sample can feel a tad awkward. Believe me, we understand! We try our best to make you comfortable because these tests are such a valuable tool for keeping an eye on your kidney health. You might also hear them called renal function tests – “renal” is just the medical term for kidney.
Why Your Kidneys Are So Important
Your kidneys do more than just filter waste. They’re part of your urinary system, and most of us have two, tucked away in the back of our abdomen, kind of under the ribcage.
Beyond filtering, they also play a key role in:
- Producing hormones that help regulate your blood pressure.
- Making erythropoietin, a hormone vital for producing red blood cells (the ones that carry oxygen all around your body).
- Activating Vitamin D, which is crucial for healthy bones and muscles.
When Might We Suggest Kidney Function Tests?
We often recommend these tests if you have conditions known to affect the kidneys, like diabetes or high blood pressure (hypertension). It helps us monitor how these conditions are impacting your kidneys and adjust your care if needed.
Sometimes, though, symptoms might pop up that make us think, “Hmm, let’s check the kidneys.” These can include:
- Seeing blood in your pee (we call this hematuria).
- Noticing your urine is foamy (this could point to proteinuria, or protein in the urine).
- A burning feeling or pain when you pee (dysuria).
- Feeling like you need to pee really often.
- Peeing less than you normally would (oliguria).
- Having trouble getting the stream started.
- Swelling in your body, especially ankles, legs, or around your eyes (edema).
- Feeling incredibly tired or fatigued.
- Nausea and vomiting.
- A noticeable loss of appetite.
Diving into the Different Kidney Tests
There isn’t just one single “kidney function test.” We usually pick and choose from a few, depending on what we’re looking for.
Blood Tests for Your Kidneys
These are pretty common:
- Blood Urea Nitrogen (BUN): This test measures the amount of nitrogen (a waste product from protein breakdown) in your blood.
- Estimated Glomerular Filtration Rate (eGFR): This is a calculation based on your serum creatinine level, age, sex, and sometimes height and weight. It gives us a good estimate of how well your kidneys are filtering.
- Serum Creatinine: Creatinine is a waste product that comes from normal muscle wear and tear. Healthy kidneys filter it out, so if it’s building up in your blood, it can be a sign your kidneys aren’t working at their best.
24-Hour Urine Tests
Sometimes, we need to look at your urine over a whole day:
- Microalbuminuria: This one specifically looks for tiny amounts of a protein called albumin in your urine. It can be an early sign of kidney damage, especially in people with diabetes.
- Urinalysis: This is a general check-up for your pee. We look for things like blood, protein, how acidic it is, its concentration (specific gravity), and if there are any tiny particles like casts (tube-shaped particles) or crystals.
Getting Ready for Your Kidney Tests
How you prepare really depends on the specific test.
For some blood tests, we might ask you to:
- Fast (not eat or drink anything but water) for several hours beforehand. If this is needed, we’ll definitely let you know.
- It might sound a bit odd, but keeping your arms moisturized can sometimes make it a bit easier for the phlebotomist (the person drawing your blood) to find a vein.
And please, if you’re nervous about needles (it’s called trypanophobia, and it’s very common!), tell us. We can talk through ways to help you feel more relaxed.
For urine tests, there’s usually not much special preparation. Drinking an extra glass of water before you come in can help make sure you can provide enough of a sample. Oh, and if you’re having your period, it’s good to let us know, as menstrual blood can sometimes affect the results.
What Happens During the Tests?
For a 24-hour urine collection, you’ll do this at home. We’ll give you a special container.
- The morning you start, go ahead and pee in the toilet like usual when you first wake up. Don’t collect that one.
- For the rest of that day and night, every time you pee, collect it in the container.
- The next morning, when you first wake up, collect that urine in the container too. That’s your last one.
- Then, you just bring the container back to our office or the lab.
For a blood test, you’ll pop into the clinic or a lab. A phlebotomist will clean an area on your arm (usually the inside of your elbow) and then use a small needle to draw a bit of blood into a test tube. It’s usually pretty quick.
What to Expect Afterwards
Kidney function tests are generally very safe. After a blood draw, some people might notice:
- A little bruising where the needle went in.
- Feeling a bit dizzy or lightheaded for a moment.
- Feeling a bit tired.
These things usually pass quickly. But if you have pain, ongoing fatigue, or any other symptoms that worry you, please give us a call.
Understanding Your Kidney Function Test Results
The results tell us if your kidneys are working as they should. Two key numbers we often look at are your estimated glomerular filtration rate (eGFR) and your urine albumin-creatinine ratio (uACR).
Estimated Glomerular Filtration Rate (eGFR)
We measure eGFR in milliliters of blood cleaned per minute per body surface area (mL/min/1.73m²).
- For adults, an eGFR of 90 or higher is generally considered normal.
- An eGFR between 60 and 89 might suggest some mild kidney damage, but your kidneys could still be functioning reasonably well. We’d want to keep an eye on this.
- An eGFR below 60 for three months or more can be an indicator of chronic kidney disease (CKD).
It’s worth noting that eGFR naturally tends to get a bit lower as we age. It’s a normal part of the aging process, even if you don’t have kidney disease. For example:
- Age 20-29: Average eGFR around 116
- Age 30-39: Average eGFR around 107
- Age 40-49: Average eGFR around 99
- Age 50-59: Average eGFR around 93
- Age 60-69: Average eGFR around 85
- Age 70+: Average eGFR around 75
Urine Albumin-Creatinine Ratio (uACR)
The uACR measures the amount of albumin (a protein) compared to creatinine (a waste product) in your urine. We measure this in milligrams of albumin per gram of creatinine (mg/g).
- A uACR less than 30 mg/g is typically what we like to see.
- A uACR of 300 mg/g or higher is a serious sign and means there’s a very high risk of kidney failure. It also puts you at greater risk for heart attack or stroke.
When Will I Get My Results?
This can vary. Sometimes, we can discuss results with you on the same day. Other times, samples go to an external lab, and it might take a few days. We’ll always let you know when to expect them.
What If My Results Show Early Kidney Disease?
If your kidney function tests point towards early kidney disease, please don’t panic. The first step is a conversation. We’ll talk about what the results mean for you and what treatment options are available. This might involve medications to help manage high blood pressure, for instance. We might also refer you to a nephrologist, a doctor who specializes in kidney diseases.
If your results are a bit off or unexpected, we’ll likely suggest more regular kidney function tests to keep a close watch on your kidney health.
When to Call Your Doctor
If you know you have chronic kidney disease, or you’re at high risk, give us a call if you notice any of these:
- Peeing more than usual.
- Bloody or foamy pee.
- Extreme tiredness.
- Muscle spasms or cramps.
- Nausea or vomiting.
- Shortness of breath.
- Swelling, especially in your hands, feet, or ankles.
Can Drinking Water Lower Creatinine?
That’s a common question! Drinking a lot of water right before a blood test can temporarily dilute your blood and slightly lower your creatinine reading. But, and this is a big but, it doesn’t fix any underlying kidney problems or improve your kidney function long-term. If you have early kidney disease, working with a nephrologist and a renal dietitian (a dietitian specializing in kidney health) to develop a kidney-friendly eating plan is far more effective.
Take-Home Message: Kidney Function Tests
Here’s what I really want you to remember about kidney function tests:
- They are simple blood and/or urine tests to check how well your kidneys are filtering waste.
- We might recommend them if you have conditions like diabetes or high blood pressure, or if you have symptoms like changes in urination, swelling, or fatigue.
- Key results include your eGFR (how well your kidneys filter) and uACR (protein in urine).
- Normal eGFR is generally above 90, but it naturally declines a bit with age. An eGFR below 60 may indicate kidney disease.
- A uACR below 30 mg/g is ideal. Higher levels can signal kidney damage.
- Early detection of kidney issues through these tests allows for timely management.
It’s all about understanding what’s going on inside your body. These tests help us do just that.
You’re not alone in this. We’re here to guide you through understanding your health, one step at a time.
