Kidney function is monitored primarily through two lab tests: a blood test that estimates how well your kidneys filter waste (called eGFR) and a urine test that checks for protein leaking into your urine. Together, these two numbers give the clearest picture of kidney health over time. An eGFR above 60 and no protein in the urine generally signals normal function, while results outside those ranges trigger closer tracking and additional tests.
eGFR: The Core Blood Test
The estimated glomerular filtration rate, or eGFR, is the single most important number for kidney monitoring. It estimates how many milliliters of blood your kidneys filter per minute, calculated from a simple blood draw that measures creatinine, a waste product your muscles produce at a fairly steady rate. The current standard formula, adopted in 2021 after the National Kidney Foundation and American Society of Nephrology reviewed more than 20 approaches, no longer adjusts for race. The previous race-based equation had contributed to health disparities by systematically overestimating kidney function in Black patients.
An eGFR of 90 or above is considered normal. Below 60, the risk of death, cardiovascular disease, and progression to kidney failure rises meaningfully. Below 15 represents end-stage kidney failure. For people whose eGFR falls in the borderline zone of 45 to 59 but who have no other signs of kidney damage, doctors often order a second blood marker called cystatin C to confirm or rule out chronic kidney disease (CKD). Cystatin C is less affected by muscle mass, diet, and body composition than creatinine, making it a useful tiebreaker. If the eGFR calculated from cystatin C comes back above 60, CKD is not confirmed, even if the creatinine-based estimate was lower.
BUN and Creatinine Together
Blood urea nitrogen (BUN) is another waste product measured alongside creatinine. The normal range for BUN is 5 to 20 mg/dL, though it fluctuates more than creatinine because it’s influenced by protein intake, hydration, and liver function. What matters most is the ratio between the two values. In moderate to advanced kidney disease, BUN and creatinine tend to rise in roughly a 10-to-1 ratio. If BUN climbs much higher than that ratio would predict, it points to something beyond the kidneys, like dehydration, high protein intake, or gastrointestinal bleeding, prompting doctors to investigate further.
Urine Albumin: Catching Damage Early
Healthy kidneys keep protein in the blood where it belongs. When the filtering units are damaged, albumin (the most abundant blood protein) starts leaking into urine. The standard test is the urine albumin-to-creatinine ratio, or UACR, taken from a single urine sample. A result above 30 mg/g signals albuminuria and counts as a marker for CKD regardless of eGFR. Levels between 30 and 300 mg/g indicate moderate albumin leakage, sometimes called microalbuminuria. Above 300 mg/g is considered severe.
Tracking UACR over time does more than confirm a diagnosis. In a large cohort of CKD patients, higher UACR at diagnosis was associated with greater risk of losing half of kidney function, needing dialysis, or dying. On the flip side, patients who lowered their UACR through treatment had a lower risk of progressing to kidney failure. That makes UACR one of the few kidney markers where improvement directly correlates with better outcomes.
How Often Testing Should Happen
If you have no known kidney problems, a routine annual checkup that includes a basic metabolic panel and urinalysis is typically sufficient. For people with diabetes, high blood pressure, or a family history of kidney disease, annual screening with both eGFR and UACR is standard practice. Once CKD is diagnosed, the monitoring schedule tightens based on how advanced the disease is and how much protein is in the urine.
A prospective study calculated optimal follow-up intervals for each CKD stage:
- Stage 3A (eGFR 45–59): every 6 months
- Stage 3B (eGFR 30–44): every 3 to 4 months
- Stage 4 (eGFR 15–29): every 2 months
- Stage 5 (eGFR below 15): roughly monthly
Albuminuria severity shifts these intervals further. Patients with severe albuminuria at any stage need more frequent monitoring. Those without albuminuria could safely stretch to about every 8 to 9 months even at stage 3A. The pattern is intuitive: the more advanced the disease or the more protein in the urine, the faster things can change.
Electrolytes That Signal Trouble
As kidneys lose filtering capacity, they struggle to balance key minerals in the blood. Potassium, phosphorus, sodium, and calcium all shift in predictable ways. An 11-year follow-up study found that patients with rising potassium and phosphorus combined with falling sodium and calcium had a 3.68-fold higher risk of eventually needing dialysis compared to patients whose electrolytes stayed stable. Their kidney function also declined faster, losing an average of 2.6 points of eGFR per year.
These electrolyte shifts tend to become clinically significant in stages 3B and beyond, which is why routine blood panels in later CKD stages include potassium, phosphorus, and calcium. High potassium is the most immediately dangerous because it can cause heart rhythm problems. High phosphorus works more slowly, pulling calcium from bones and contributing to vascular calcification over months and years.
Blood Pressure and Blood Sugar Targets
Kidney monitoring isn’t just about the kidneys themselves. The two conditions most responsible for kidney damage, diabetes and high blood pressure, need their own tracking. Current guidelines recommend keeping blood pressure below 130/80 mmHg and hemoglobin A1c below 7% to slow CKD progression in people with diabetes. Hitting both targets simultaneously reduces the strain on the kidney’s filtering units and lowers cardiovascular risk, which matters because people with CKD are more likely to develop heart disease than they are to reach end-stage kidney failure.
When Imaging Comes Into Play
Blood and urine tests measure function. Ultrasound measures structure. It’s the first-line imaging test when kidney disease is newly detected or when there’s an unexplained drop in function. Ultrasound uses no radiation and produces real-time images, making it safe for repeated use.
Doctors look at two main measurements. Normal kidney length is roughly 10 to 12 cm; a kidney measuring 8 cm or less is associated with kidney failure. Normal cortical thickness (the outer layer that does the filtering) is 7 to 10 mm. When it thins below that, it suggests progressive disease, scarring, or fibrosis. Bilateral shrinkage of both kidneys points to advanced, likely irreversible damage. Ultrasound also detects structural problems like cysts, stones, or blockages that blood tests alone would miss.
At-Home Urine Dipsticks and Their Limits
Over-the-counter urine dipsticks are inexpensive and widely available, and they can detect protein in urine. But their accuracy has real limitations. When tested against the lab-standard UACR threshold of 30 mg/g, dipsticks reading “trace” caught only 63.5% of cases with true albuminuria, missing more than a third. At the “1+” reading, sensitivity dropped further to 46%, meaning more than half of people with early kidney damage would get a falsely reassuring result.
Specificity is the dipstick’s strength: when it reads positive, it’s right about 82 to 94% of the time. So a positive dipstick result is worth taking seriously and following up with a lab test. But a negative result doesn’t rule out early kidney problems. For anyone at elevated risk, lab-based UACR testing remains far more reliable than home screening.
Putting It All Together
A complete kidney monitoring picture combines eGFR from blood work, UACR from a urine sample, electrolyte trends over time, and blood pressure and blood sugar control if you have diabetes or hypertension. Ultrasound fills in the structural side when there’s reason for concern. No single test tells the whole story. eGFR can be normal while albumin is already leaking, and albumin can be normal while eGFR is declining. Tracking both together, at intervals matched to your risk level, is what catches kidney disease early enough to slow it down.