- 01Kidney function is two numbers, not one
A kidney panel scores filtering (eGFR) and damage (urine albumin) separately. Because protein can leak into the urine while eGFR still reads normal, checking only the filtering number can miss early kidney disease.
- 02One bad result is not a diagnosis
A single low eGFR or high ACR only counts toward chronic kidney disease if it stays abnormal past 3 months. Dehydration, a short illness, or certain drugs can move the numbers temporarily, which is why the finding gets repeated before it means anything lasting.
A kidney function test, sometimes called a renal panel, is a set of numbers answering two separate questions: how fast your kidneys filter your blood, and whether they are leaking or damaged. Read together, they tell you far more than any single value does.
'Renal' means kidney, so a renal function test and a kidney function test are the same order. Most of it comes from a routine blood draw. The piece often left off is a urine test, and it is often the most telling.
Your kidneys do two jobs a lab can score. They filter waste out of your blood, and they hold back things your body needs, like the blood protein albumin. A kidney panel measures both: filtering with eGFR, and the barrier with a urine test.
Kidney function is scored on two axes at once: how fast you filter, measured by eGFR (estimated glomerular filtration rate), and how much protein leaks into your urine, measured by the albumin-to-creatinine ratio. You need both, because damage often shows in the urine before the filtering number drops. 2
Why eGFR alone can miss early damage
In many people, the earliest sign of kidney trouble is a small amount of albumin slipping into the urine while eGFR still reads a comfortable 90. If a report only shows eGFR, that early signal is invisible. Check both axes and the leak shows up years sooner.
Here is what each number on a kidney panel measures, and the thing that most often throws it off.
| Test | What it measures | What throws it off |
|---|---|---|
| Creatinine | A muscle waste product in your blood; its level rises as filtering falls | Muscle mass, a big meat meal, creatine supplements, and drugs such as trimethoprim or cimetidine |
| eGFR | An estimate of filtering rate, calculated from creatinine, age, and sex | Least reliable near normal, and off by more than 30 percent in roughly 1 in 7 to 1 in 10 people |
| Cystatin C | A second filtering marker, from a protein all cells make, that muscle mass does not distort | Thyroid disease, steroids, inflammation, higher body fat, and smoking can raise it |
| BUN | Blood urea nitrogen, a waste left from protein breakdown | Dehydration, a high-protein diet, and gut bleeding raise it apart from kidney function |
| Urine ACR | How much albumin (a blood protein) leaks into your urine; the damage signal | A urinary infection, hard exercise, or menstrual blood can raise it briefly |
Creatinine
Creatinine is a waste product your muscles make at a steady rate and your kidneys clear, so its level in blood climbs as filtering falls. The catch is sensitivity. As the creatinine page puts it, one clean reading does not rule out trouble:
Serum creatinine can sit inside the normal range while up to half of your kidneys' filtering capacity is already gone.
Typical adult ranges run about 0.7 to 1.3 mg/dL in men and 0.6 to 1.1 mg/dL in women. A big steak dinner, creatine supplements, or drugs such as trimethoprim can nudge it up without your kidneys changing what they do, so the number is read in context, not in isolation.
eGFR
eGFR (estimated glomerular filtration rate) is exactly that, an estimate, not a direct measurement. As the eGFR page puts it, it 'turns your creatinine, age, and sex into one number estimating how many millilitres your kidneys filter per minute, and below 60 for more than three months is the line that marks chronic kidney disease.' It is least reliable near normal, and it lands more than 30 percent away from a measured filtration rate in roughly 1 in 7 to 1 in 10 people 3, which is one reason a borderline result gets confirmed rather than trusted on its own. The 2021 equation also dropped race from the math, so the same creatinine now returns one eGFR for everyone 3. If you are holding a creatinine value, the eGFR page has a calculator that does the arithmetic.
Cystatin C
Cystatin C is a second way to estimate filtering, using a small protein that every cell makes at a steady rate. Because muscle mass does not distort it the way it distorts creatinine, it works as a tie-breaker when a creatinine-based eGFR does not match the person, for example someone very muscular, very frail, or an amputee. It has its own quirks: thyroid disease, steroid medicines, inflammation, and smoking can raise it 4. The most accurate estimate combines both markers.
BUN (blood urea nitrogen)
BUN, short for blood urea nitrogen, measures a waste product left when your body breaks down protein. On its own it is a rough kidney signal, because dehydration, a high-protein diet, and bleeding in the gut push it up regardless of filtering. It is most useful next to creatinine, as the BUN-to-creatinine ratio, which helps separate dehydration from kidney injury.
Urine albumin-to-creatinine ratio (ACR)
The urine albumin-to-creatinine ratio (ACR) is the damage axis. Albumin is a blood protein too big for healthy kidneys to leak, so finding it in urine points to a filter that is starting to give way. It is graded in three bands: A1 under 30 mg/g, A2 from 30 to 300, and A3 above 300 2. This is the test most often left off a basic panel, and the one that catches early trouble first.
Where an example urine ACR fallsmg/g
The actual numbers
Here are the cutoffs behind the labels. Treat them as categories, not verdicts: your clinician reads them against your age, muscle mass, medicines, and any past results.
| Test | Unit | Reassuring | Watch | Flagged |
|---|---|---|---|---|
| eGFR | mL/min/1.73m2 | 60 or above (G1 to G2) | 45 to 59 (G3a) | Below 45 (G3b to G5) |
| Urine ACR | mg/g | Under 30 (A1) | 30 to 300 (A2) | Above 300 (A3) |
| Serum creatinine | mg/dL | About 0.7 to 1.3 (men), 0.6 to 1.1 (women) | Just above your lab's range | Well above range, or rising fast |
| BUN | mg/dL | About 7 to 20 | Mild elevation | High with a high BUN-to-creatinine ratio |
| Cystatin C | mg/L | About 0.6 to 1.0 | Borderline | Above range |
'Reassuring' and 'optimal' are not the same. A lab may not flag an eGFR of 62 or an ACR of 25, yet risk still climbs across the higher end of the normal band, and an eGFR of 60 to 89 (stage G2) is common with age but worth watching if the urine shows a leak. The point of the two axes is that a value can be inside the reference range on one and abnormal on the other.
CKD is defined as abnormalities of kidney structure or function, present for more than 3 months, with implications for health.KDIGO 2024 Clinical Practice Guideline for CKD
That 3-month rule is why a single low eGFR is not chronic kidney disease. A stomach bug, a day of poor fluid intake, or a new medicine can drop the number for a week or two 1. The finding has to persist on a repeat test before it earns the label, which is also why panic over one printout rarely helps.
What a pair of results suggests
| eGFR | Urine ACR | What the pair suggests |
|---|---|---|
| 60 or above | Under 30 | Filtering and barrier both look intact; retest on the schedule your risk calls for |
| 60 or above | 30 or above | Possible early damage the eGFR alone would miss; worth bringing to your clinician |
| Under 60 | Under 30 | Reduced filtering without a leak; confirm it persists past 3 months and rule out acute causes |
| Under 60 | 30 or above | Both axes abnormal, the higher-risk pattern; warrants medical review |
The two axes together form the KDIGO risk map, a grid of GFR category down one side and albuminuria category across the top 2. Your box on that grid, not any one number, is what tracks your risk over time.
How it is tested, and how often
Most of a kidney panel is a single blood draw. Creatinine, eGFR, and BUN usually need no fasting, though they are often ordered inside a metabolic panel that also checks glucose or cholesterol, and those can call for fasting, so follow the instructions for the whole order. The urine ACR is a separate sample, ideally a first-morning urine, and it is frequently left off unless you or your clinician ask for it. A basic metabolic panel is inexpensive and widely covered.
Ask about a yearly eGFR and urine ACR if any of these apply to you:
- Diabetes or high blood pressure
- Heart disease or a past stroke
- A first-degree relative with kidney failure
- Long-term use of medicines your kidneys clear
Kidney failure clusters in families, so first-degree relatives of someone on dialysis or with a transplant are worth checking sooner. Whatever the trigger, an off result is repeated before it is acted on, to see whether it holds past 3 months.
The uric acid connection
Your kidneys clear about two-thirds of your body's uric acid 5, with the gut handling the rest, so sluggish filtering and high urate tend to travel together. That link is why high uric acid shows up alongside reduced kidney function, and why chronic gout and kidney disease so often overlap. The rest of the kidney topic breaks down each marker in depth.
Link · NIDDK (National Institute of Diabetes and Digestive and Kidney Diseases)Chronic kidney disease tests and diagnosisThe US government explainer on the eGFR and urine albumin tests, who should be checked, and what the results mean.niddk.nih.gov
Citations
- KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney International 2024;105(4S):S117-S314.
- KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int Suppl 2013;3:1-150 (CKD definition, GFR and albuminuria staging, cystatin C confirmation).
- Inker LA, Eneanya ND, Coresh J, et al. New Creatinine- and Cystatin C-Based Equations to Estimate GFR without Race. N Engl J Med 2021;385:1737-1749.
- Stevens LA, Schmid CH, Greene T, et al. Factors other than glomerular filtration rate affect serum cystatin C levels. Kidney Int 2009;75(6):652-660 (thyroid disease, steroids, inflammation, adiposity, and smoking as non-GFR determinants).
- Maiuolo J, Oppedisano F, Gratteri S, Muscoli C, Mollace V. Regulation of uric acid metabolism and excretion. Int J Cardiol 2016;213:8-14 (renal clearance of roughly two-thirds of urate, with the intestine handling the remainder).
Educational context only, not medical advice or a diagnosis. Always discuss your results with a clinician.