Checking your kidneys typically involves 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 urine. Both can be done at a routine doctor’s visit, and together they give a reliable picture of kidney health. Most kidney disease has no symptoms in its early stages, so testing is the only way to catch problems before they progress.
The Two Core Tests
The blood test measures a waste product called creatinine, which your muscles produce at a fairly steady rate. Healthy kidneys filter creatinine out of your blood efficiently, so when levels climb, it signals that your kidneys are struggling. Normal serum creatinine ranges from 0.74 to 1.35 mg/dL for adult men and 0.59 to 1.04 mg/dL for adult women.
Your doctor won’t just look at creatinine alone. That number gets plugged into a formula along with your age and sex to produce an estimated glomerular filtration rate, or eGFR. Think of eGFR as a score for how efficiently your kidneys clean your blood. A score of 90 or above is normal. Below 60 suggests kidney disease, and below 15 means kidney failure. The eGFR is more useful than raw creatinine because creatinine levels naturally vary based on muscle mass, diet, and body size.
The urine test looks for albumin, a protein that healthy kidneys keep in the blood. When kidneys are damaged, albumin leaks through into urine. The result is expressed as an albumin-to-creatinine ratio (ACR). A value under 30 is normal. Between 30 and 300 indicates early kidney damage, sometimes called microalbuminuria. Above 300 signals more significant damage. This test can detect problems years before eGFR starts to drop, making it one of the earliest warning signs available.
What eGFR Numbers Mean in Practice
Kidney disease is classified into five stages based on eGFR:
- Stage 1 (eGFR 90+): Normal filtration, but other signs of damage are present, such as protein in urine
- Stage 2 (eGFR 60–89): Mildly decreased function
- Stage 3a (eGFR 45–59): Mild to moderate decrease
- Stage 3b (eGFR 30–44): Moderate to severe decrease
- Stage 4 (eGFR 15–29): Severe decrease
- Stage 5 (eGFR below 15): Kidney failure
An important detail: an eGFR of 60 to 89 by itself does not qualify as kidney disease. You need additional evidence of damage, like albumin in your urine or abnormalities on imaging, for stages 1 or 2 to count as a diagnosis. Many older adults have an eGFR in the 60s with perfectly healthy kidneys for their age.
The BUN Test
Another blood marker your doctor may check is blood urea nitrogen, or BUN. Urea is a waste product from protein digestion, and healthy kidneys clear it efficiently. The normal range is 5 to 20 mg/dL. BUN on its own is less specific than creatinine because dehydration, high-protein diets, and certain medications can all push it higher without any kidney problem.
Where BUN becomes useful is in the ratio to creatinine. A ratio around 10:1 is typical. If BUN is disproportionately high compared to creatinine, it often points to something outside the kidneys, like dehydration or a blockage in the urinary tract, rather than kidney disease itself. Your doctor uses the ratio as a clue to figure out what’s driving abnormal results.
When Electrolytes Signal a Problem
A basic metabolic panel, which is part of routine bloodwork, also checks electrolyte levels. Healthy kidneys keep potassium, sodium, and phosphorus in a tight balance. As kidney function declines, potassium can build up in the blood because the kidneys can no longer remove it effectively. High potassium is particularly dangerous because it can cause heart rhythm problems and muscle weakness.
Phosphorus follows a similar pattern. Damaged kidneys struggle to clear it, and excess phosphorus pulls calcium out of bones over time. These electrolyte shifts generally don’t appear until kidney disease reaches stage 3 or later, so they’re less useful for early screening but important for monitoring once a problem is known.
Imaging Tests
When blood or urine results raise concerns, imaging helps identify structural problems like kidney stones, cysts, tumors, or changes in kidney size. Ultrasound is the usual first step. It uses no radiation, is widely available, costs less than other options, and can be done at the bedside. For detecting kidney stones, ultrasound has a pooled sensitivity of about 45%, meaning it misses roughly half of small stones, though it performs better for larger ones (around 77% sensitivity in some studies).
CT scans are the gold standard for stones and structural detail, with sensitivity exceeding 95%. They also measure stone size more accurately. Ultrasound tends to overestimate stone size by about 1.8 mm on average, which can affect treatment decisions. The tradeoff is that CT involves radiation exposure and higher cost, so doctors typically reserve it for situations where ultrasound results are unclear or when precise measurements matter for planning treatment.
At-Home Screening Options
Home urine test kits that check for albumin are now available and can be a useful first step if you want to screen yourself between doctor visits. Some newer options pair a urine dipstick with a smartphone app that reads and interprets the color changes on the strip, then lets you share results with your doctor. The National Kidney Foundation has supported research into these tools as a way to improve screening rates, particularly for people at higher risk who may not get tested regularly.
These kits are best thought of as a screening tool, not a diagnosis. A positive result should be confirmed with a lab-based albumin-to-creatinine ratio test. And home kits can only check one side of the equation. You still need a blood draw to get your eGFR, which no at-home test can provide.
Who Should Get Tested and How Often
If you have diabetes or high blood pressure, the two leading causes of kidney disease, annual screening is strongly recommended. For people with type 2 diabetes, screening should start at diagnosis and continue every year. For type 1 diabetes, annual screening should begin after five years with the disease. Both groups should get a urine albumin test and a blood creatinine test (for eGFR) each year.
Other factors that increase your risk and warrant regular screening include a family history of kidney disease, heart disease, obesity, and being over 60. If none of these apply to you, kidney function is still checked as part of routine bloodwork during a standard physical, so you’re likely being screened without realizing it.
Symptoms That Suggest Kidney Trouble
Early kidney disease is almost always silent. By the time symptoms appear, significant damage has often already occurred. That said, knowing what to look for matters. Swelling in the feet, ankles, and legs is one of the more recognizable signs, caused by the kidneys failing to remove excess fluid. A sudden increase in body weight can also indicate fluid retention. In later stages, fluid can build up in the lungs, causing shortness of breath.
Other symptoms of advancing kidney disease include persistent nausea, loss of appetite, muscle cramps, dry and itchy skin, trouble sleeping, and changes in urination, either producing too much or too little. These symptoms overlap with many other conditions, which is why testing remains far more reliable than waiting to feel something wrong.
When a Biopsy Is Needed
In specific situations, blood and urine tests alone can’t explain what’s happening inside the kidneys. A kidney biopsy, where a small tissue sample is taken with a needle, is reserved for cases like unexplained rapid loss of kidney function, large amounts of protein in the urine with no clear cause, blood in the urine originating from the kidneys, or kidney involvement in systemic diseases like lupus. It’s not a routine screening tool. Doctors order it when they need to see the microscopic structure of kidney tissue to choose the right treatment.