Your kidney lab report probably has four numbers that matter most: eGFR, creatinine, BUN, and ACR (urine albumin-to-creatinine ratio). Together, they give a reasonably complete picture of how well your kidneys are filtering and whether protein is leaking through. This post explains what each number measures, what the normal ranges are, why trends matter more than single readings, what you can track between lab visits, and which questions are worth bringing to your nephrologist.
A note upfront: this post is educational. It does not interpret your specific numbers or tell you whether a result is concerning. Only your doctor can do that in the context of your full history.
What eGFR, creatinine, BUN, and ACR each measure
Creatinine (serum creatinine). Creatinine is a waste product produced by normal muscle metabolism. Your kidneys filter it out of your blood and excrete it in urine. When kidney filtering slows, creatinine builds up in blood. A creatinine blood test measures how much is present. Normal ranges are roughly 0.6 to 1.2 mg/dL for adult men and 0.5 to 1.1 mg/dL for adult women, though lab reference ranges vary slightly. Creatinine is influenced by muscle mass, so someone very muscular may have a higher baseline, and someone with low muscle mass may have a lower baseline, independent of kidney function.
eGFR (estimated glomerular filtration rate). eGFR is calculated from serum creatinine, adjusted for age and sex. It estimates how much blood your kidneys filter per minute, expressed in mL/min/1.73m². Healthy adult eGFR is above 90. Values below 60 sustained for three or more months meet the clinical criteria for chronic kidney disease. According to the National Kidney Foundation, eGFR is the most commonly used marker of kidney function in clinical practice.
BUN (blood urea nitrogen). BUN measures a nitrogen-containing waste product from protein metabolism. Your kidneys filter it out. Normal ranges are typically 7 to 20 mg/dL, though this varies. BUN rises with reduced kidney function, but also rises with dehydration, high-protein diets, and certain medications. The ratio of BUN to creatinine can help distinguish between these causes: a high ratio often suggests dehydration rather than true kidney dysfunction.
ACR (urine albumin-to-creatinine ratio). ACR measures how much albumin (a protein) is leaking into urine, normalized to urine creatinine concentration to account for how dilute or concentrated the sample is. Healthy kidneys keep albumin in blood. Leak means the kidney's filtering units may be stressed or damaged. An ACR below 30 mg/g is normal. 30 to 300 is "microalbuminuria," an early marker of kidney stress. Above 300 is clinically significant proteinuria. ACR is often the earliest lab sign of kidney trouble, showing up before eGFR drops.
Normal ranges for each
The specific normal ranges depend on the lab running the test, but the general ranges most U.S. labs use are:
Serum creatinine: 0.6–1.2 mg/dL (men), 0.5–1.1 mg/dL (women).
eGFR: Above 90 is normal. 60–89 is "mildly decreased" (consistent with stage 2 CKD if there's also evidence of damage). 30–59 is "moderately decreased" (stage 3). Below 30 is "severely decreased" (stages 4 and 5).
BUN: 7–20 mg/dL. Values above 20 often indicate dehydration, high protein intake, or reduced kidney function.
BUN-to-creatinine ratio: 10:1 to 20:1 is typical. A ratio above 20:1 often suggests dehydration. A ratio below 10:1 can suggest severe liver disease or low protein intake.
ACR: Below 30 mg/g is normal. 30–300 is microalbuminuria. Above 300 is macroalbuminuria or clinical proteinuria.
Reference ranges are population averages, not personal guarantees. A value just outside the range isn't automatically concerning, and a value inside the range isn't automatically fine. The context of your own history matters more than where any single reading sits relative to the population.
Why the trend matters more than a single reading
This is the single most important principle in interpreting kidney labs.
A creatinine of 1.3 mg/dL in someone whose baseline has always been 1.0 is a meaningfully different situation than someone whose baseline has always been 1.3. The first suggests a change worth investigating. The second is just that person's normal.
Similarly, an eGFR that dropped from 65 to 58 over a year tells a different story than an eGFR that's been steady at 58 for five years. The first suggests progression and deserves clinical attention. The second is stable disease that may not need aggressive intervention.
This is why one of the most valuable things you can do for your own kidney health is keep a personal record of your labs across years. Your doctor has access to this too, but having it organized in a way you can see at a glance often surfaces patterns that get missed in brief appointments.
Lab-to-lab variation is real. The same blood sample run through different labs can produce results that differ by 10 to 15 percent. This is why consistent lab use (using the same lab across testing) is more useful than switching labs for each draw. When labs change, some variation in results is expected even if your actual kidney function hasn't changed.
Hydration status at the time of the draw also affects results. A creatinine measured while you're mildly dehydrated will be higher than the same person's creatinine when well-hydrated. This is one reason a single unexpectedly high reading often resolves on repeat testing — the first draw may have been a hydration artifact. The post on GLP-1 and kidney labs covers this specifically for people on GLP-1 medications who see lab shifts.
Home tracking between lab visits
You can't measure kidney function at home, but you can track the inputs and signals that most affect the lab numbers.
Urine color and patterns. Daily observation of color, any foam, and general urination frequency catches shifts that don't show in labs for weeks. Apps like Urivia let you log these patterns over time, which means you can bring specific data to your next appointment rather than vague recollections.
Blood pressure. A home cuff costs $30 to $80 and is accurate enough for trend tracking. High blood pressure damages kidneys silently over years. Keeping readings in target range is one of the most directly kidney-protective actions available.
Weight. A consistent morning weight catches fluid retention early. Sudden weight gain over two to three days can precede lab changes by weeks.
Medications. Keep a running list of everything you take, including over-the-counter. NSAIDs, certain antibiotics, contrast dyes from imaging studies, and some blood pressure medications all affect kidney labs. Having this list available at lab time helps your doctor interpret results.
Symptoms. Log anything new: swelling, fatigue outside your baseline, persistent foam, changes in urination. Pattern recognition across weeks is more useful than reacting to individual observations.
The daily kidney health checklist covers the full home tracking routine in detail.
Questions to bring to your nephrologist
Lab results are more useful when discussed in a real conversation, not just read off a patient portal. The questions worth bringing:
What's my trend compared to my baseline from before my current treatment? A single value matters less than the trajectory.
Is this change consistent with dehydration, medication effects, or true progression? The BUN-to-creatinine ratio and ACR can help distinguish between these.
How often should I have these labs drawn given my current status? Frequency varies based on stage, risk factors, and medication regimen.
Do I have any risk factors that should change the frequency of ACR testing specifically? Some patients benefit from more frequent albumin monitoring.
Is my current blood pressure target still right for my kidney function? Targets sometimes shift as CKD progresses.
Are any of my current medications contributing to lab changes? Some medications routinely elevate creatinine without causing kidney damage.
Should I see a renal dietitian? At certain stages, nutrition specialists can meaningfully improve outcomes.
What should I do at home to support these numbers? Hydration, activity, medication adherence all play roles.
What symptom changes should I report between visits? Knowing the specific warning signs for your situation prevents unnecessary worry and prevents missed warning signs.
The post on questions for your nephrologist has an expanded version of this list for appointments that go deeper.
When to see a doctor
A blog post can't examine you. Reach out to your nephrologist or primary care doctor if: your most recent labs showed meaningful changes from baseline and you don't understand what they mean; new symptoms have appeared (swelling, persistent foam, fatigue, urination changes); you're unsure whether your current medications are affecting your kidney labs; you've had a rough GI episode, severe dehydration, or new contrast imaging since your last labs.
Go to urgent care or the ER for: severe swelling with shortness of breath; confusion with fatigue; chest pain; severe decrease in urination; any signs of acute illness on top of chronic kidney disease.
How to track this yourself
Personal record-keeping for kidney labs pays off across years, not weeks. Keep a simple log of every eGFR, creatinine, BUN, and ACR result with dates. Note any lab changes (switching facilities) since inter-lab variation is real.
Apps like Urivia let you log urine color, hydration, and symptoms between visits, which helps fill in the picture that labs alone miss. The CKD stages post covers how these lab numbers map to the clinical staging system.
Frequently asked questions
What's a normal eGFR by age?
eGFR naturally declines slightly with age, but "normal" is still above 90 for most adults. Some decline after age 60 is common and not necessarily pathological. Values between 60 and 89 without other evidence of kidney damage may simply reflect aging. Values below 60 sustained for more than three months meet the criteria for chronic kidney disease regardless of age.
Why does my creatinine vary between lab visits?
Several reasons. Hydration status at the time of the draw affects results. Lab-to-lab variation can be 10 to 15 percent. Muscle mass changes affect creatinine production. Recent intense exercise can temporarily elevate creatinine. High-protein meals in the 24 hours before the draw can shift BUN and creatinine slightly. Your doctor factors these in when looking at single readings versus trends.
Is BUN more important than creatinine?
Neither is "more important" — they measure different things and are most useful together. Creatinine and eGFR give the clearest picture of filtering function. BUN adds context about dehydration and protein intake. The BUN-to-creatinine ratio is often more informative than either number alone.
What does microalbuminuria mean?
Microalbuminuria means a small amount of albumin is leaking into urine — an ACR between 30 and 300 mg/g. It's an early warning sign of kidney stress, often present before eGFR or creatinine show meaningful changes. For patients with diabetes especially, microalbuminuria is a key marker that typically prompts specific medication changes (often ACE inhibitors or ARBs) to protect kidney function.
Can I request kidney labs from my primary care doctor?
Yes. Most primary care practices can order serum creatinine, eGFR, BUN, and urine ACR without a nephrology referral. If you have risk factors (diabetes, hypertension, family history of kidney disease, certain medications), these are reasonable to request at an annual visit. If your labs show meaningful abnormalities, your primary care doctor may then refer you to a nephrologist.
How often should kidney labs be repeated?
For adults with no kidney risk factors, every two to three years is reasonable. For adults with risk factors (diabetes, hypertension, etc.), annually at minimum, sometimes more often. For diagnosed CKD, every three to six months depending on stage, with stage 3b and later often warranting quarterly monitoring. Your nephrologist sets specific frequencies based on your situation.
What if my labs have been slowly trending worse over years?
This is the situation where trend analysis matters most. A slow downward eGFR trend over several years, even if each individual value is still within range, can indicate progressive kidney disease. Your nephrologist can calculate your rate of decline and determine whether intervention (medication adjustments, dietary changes, specialist referral) is warranted. The post on CKD stages covers what happens at each progression point.