Kidney disease is tested primarily through two simple tests: a blood test that measures how well your kidneys filter waste, and a urine test that checks for protein leaking into your pee. Together, these two results give a reliable picture of kidney health and can catch problems years before symptoms appear. Most kidney disease is detected through routine lab work, not specialized procedures.
The Two Core Tests
The foundation of kidney testing comes down to one blood draw and one urine sample. The blood test measures your estimated glomerular filtration rate, or eGFR, a number that represents how efficiently your kidneys are cleaning your blood. It’s calculated using your age, sex, and the level of a waste product called creatinine in your blood. A healthy eGFR is 90 or above. The lower the number, the worse your kidneys are filtering.
The urine test is called a urine albumin-to-creatinine ratio, or uACR. Albumin is a protein that belongs in your blood, not your urine. When your kidneys are damaged, tiny amounts of albumin start slipping through into your pee. This leakage can happen early in kidney disease, often before your eGFR drops noticeably. The uACR is more sensitive than a basic urine dipstick for catching these small amounts of protein, which is why it’s the preferred screening tool.
You don’t need to fast or do anything special before either test. The blood draw is standard, and the urine sample is typically a single “spot” collection, not a 24-hour jug.
What Your eGFR Number Means
Your eGFR result is reported in milliliters per minute and corresponds to a stage of chronic kidney disease (CKD). Here’s how the stages break down:
- 90 or higher (Stage 1): Normal filtration rate. Kidney disease is only present if other signs like protein in the urine exist.
- 60 to 89 (Stage 2): Mildly reduced function. Often no symptoms.
- 45 to 59 (Stage 3a): Mild to moderate loss of function.
- 30 to 44 (Stage 3b): Moderate to severe loss.
- 15 to 29 (Stage 4): Severe loss of function.
- Below 15 (Stage 5): Kidney failure.
One important detail: your eGFR is an estimate, not a precise measurement. It represents an average of your kidney function over the past few days, similar to how a blood sugar average reflects a snapshot over time. A single reading that comes back slightly low doesn’t necessarily mean you have kidney disease. Dehydration, recent intense exercise, or certain medications can temporarily shift the result. If your number is borderline, your provider will likely repeat the test to confirm.
What Your uACR Result Means
A normal uACR is below 30 mg/g. Results between 30 and 300 mg/g indicate moderately increased albumin in your urine, sometimes called microalbuminuria. This is often the earliest detectable sign of kidney damage, particularly in people with diabetes or high blood pressure. Results above 300 mg/g signal severely increased albumin loss and suggest more significant kidney damage.
Like eGFR, a single elevated uACR doesn’t confirm kidney disease on its own. Urinary tract infections, heavy exercise, fever, and even menstruation can temporarily raise albumin levels. Providers typically want to see elevated results on at least two out of three samples over a few months before making a diagnosis.
Other Blood Tests That Support the Picture
A blood urea nitrogen (BUN) test is often ordered alongside eGFR. Urea is another waste product your kidneys filter out, and the normal range is roughly 6 to 24 mg/dL. A high BUN can point to reduced kidney function, but it’s less specific than eGFR because many other things raise it: dehydration, a high-protein diet, gastrointestinal bleeding, heart failure, certain medications, and even severe burns. BUN is useful as a supporting data point, not a standalone kidney test.
Some providers also order a cystatin C blood test, which measures a different waste product. The 2021 equation for calculating eGFR can incorporate cystatin C alongside creatinine for a more accurate estimate, particularly in people whose creatinine levels might be misleading due to unusual muscle mass (very muscular individuals or people with muscle-wasting conditions).
When Imaging Comes Into Play
Blood and urine tests detect functional problems, meaning how well your kidneys work. Imaging tests look at structural problems, meaning the physical shape and condition of your kidneys. These are not routine screening tools. They’re ordered when something specific needs investigation.
A kidney ultrasound is the most common imaging test. It’s painless, uses no radiation, and can reveal whether your kidneys are the right size and in the right position. It also detects blockages, kidney stones, cysts, and tumors. A CT scan provides more detailed three-dimensional images and is better at identifying small stones, infections, obstructions, and injuries. CT scans involve radiation exposure, so they’re reserved for situations where ultrasound doesn’t provide enough information.
Imaging is typically ordered when you have symptoms like blood in the urine, unexplained back or abdominal pain, recurrent urinary tract infections, or when blood tests already suggest kidney failure and your provider needs to understand why.
When a Biopsy Is Needed
A kidney biopsy removes a tiny piece of kidney tissue for examination under a microscope. It’s the most invasive kidney test and is reserved for situations where blood tests, urine tests, and imaging haven’t produced a clear diagnosis. Providers typically recommend a biopsy when there’s unexplained blood in the urine originating from the kidney, excessive or worsening protein in the urine, or kidney function declining without an obvious cause. It’s also used to assess transplanted kidneys that aren’t performing well.
During the procedure, a needle is guided through your back into the kidney using ultrasound. You’ll lie on your stomach, and the area is numbed with local anesthesia. The most common side effect is blood in the urine for a few days afterward. Pain at the biopsy site is typical but usually resolves within hours. Serious bleeding requiring a transfusion is rare. You’ll generally rest for several hours after the procedure and may stay for observation.
At-Home Kidney Tests
FDA-cleared home kidney tests do exist. One called Minuteful Kidney is a smartphone-enabled urine test kit that checks for albumin. You collect a urine sample at home, and the app analyzes the results. These tests can be a useful first step for people who want to screen themselves, particularly if getting to a lab is difficult. However, home tests are not a substitute for laboratory testing, and any abnormal result should be followed up with standard lab work to confirm.
Who Should Get Tested and How Often
Kidney disease often causes no symptoms until it’s advanced, which makes screening critical for people at higher risk. The two biggest risk factors are diabetes and high blood pressure, which together account for the majority of kidney disease cases.
The American Diabetes Association recommends that all people with type 2 diabetes get both an eGFR and uACR at least once a year, regardless of what treatment they’re on. For people with type 1 diabetes, annual testing should begin after five years with the condition. If you’ve already been diagnosed with chronic kidney disease, testing frequency increases to one to four times per year depending on your stage.
Beyond diabetes and high blood pressure, other factors that increase your risk include a family history of kidney disease, being over 60, having heart disease, obesity, and a history of acute kidney injury. If any of these apply to you, asking for kidney function testing during your next routine blood work is a straightforward way to check.