Albumin/Creatinine Ratio (uACR) Explained
The urine ratio KDIGO uses to grade kidney damage.
Medically reviewed by Dr. Rishi Kumar Kafle, MBBS, MD, FASN · Last reviewed June 2026
The urine albumin-to-creatinine ratio (uACR) measures how much albumin leaks into the urine, standardized against urine creatinine so a single spot sample is reliable. A normal value is under 30 mg/g. It is the albuminuria measure used in the KDIGO risk heat map, and it is one of the earliest signals that the kidney's filter is starting to leak.
What Albumin in the Urine Tells You
Albumin is the most abundant protein in blood, and a healthy glomerulus keeps almost all of it out of the urine. When the filtering membrane is damaged — by diabetes, high blood pressure, or other kidney disease — small amounts of albumin begin to slip through. Detecting that leak is valuable because it often appears before filtration measurably drops, giving an early, treatable warning. Reporting albumin as a ratio to creatinine (mg of albumin per gram of creatinine) corrects for urine dilution, so a random spot sample substitutes for a cumbersome 24-hour collection.
KDIGO Albuminuria Categories
| Category | uACR | Meaning | Older term |
|---|---|---|---|
| A1 | < 30 mg/g | Normal to mildly increased | Normoalbuminuria |
| A2 | 30–300 mg/g | Moderately increased | Microalbuminuria |
| A3 | > 300 mg/g | Severely increased | Macroalbuminuria |
The earlier term microalbuminuria matches today's A2 range — see the microalbumin/creatinine ratio. As examples, a uACR of 12 mg/g is A1 and reassuring; 120 mg/g is A2 and warrants follow-up; 450 mg/g is A3 and signals heavier protein loss.
How Albuminuria Stages CKD Risk With eGFR
Filtration and leakage are two different things, and chronic kidney disease is staged by both at once. The KDIGO “heat map” crosses a GFR category (G1 through G5) with an albuminuria category (A1 through A3) to place a patient into a risk band from low to very high. Two people can share the same eGFR yet face very different outlooks: an eGFR of 55 with A1 sits at modestly increased risk, while the same eGFR of 55 with A3 jumps to high risk. Albuminuria predicts progression and cardiovascular events independently of how fast the kidneys are filtering, which is exactly why it earns its own axis.
How the Sample Is Collected
The preferred sample is a first-morning urine, collected soon after waking, because it avoids the rise in albumin that upright posture and daytime activity can cause. A random spot sample is acceptable when a morning one is impractical. Either way, the lab measures albumin and creatinine in the same specimen and divides, so no timed collection is needed. This convenience is the whole reason uACR has largely displaced the 24-hour urine test for albuminuria — a patient can give a single cup and get a reliable number.
What Raises a uACR Temporarily
Several harmless or short-lived factors can push albumin up without meaning chronic kidney damage. Vigorous exercise in the prior 24 hours, a fever, a urinary tract infection, uncontrolled high blood sugar, heart failure, and menstrual blood can each inflate the reading. That is why a single raised value is treated as a flag, not a diagnosis. Guidelines recommend confirming an abnormal result with a repeat sample, and defining true albuminuria as a persistent elevation across two of three samples over three to six months.
Why It Matters
Because a rising uACR often precedes a falling eGFR, it is a frontline screening test in diabetes and hypertension, where catching A2 early opens a window for treatment that can slow or even reverse the trend. For someone with diabetes, an annual uACR is a standard part of kidney monitoring, and a result climbing from A1 into A2 is often the cue to start or intensify kidney-protective therapy. The same value also carries cardiovascular meaning: albuminuria independently predicts heart disease risk, so the number speaks to more than the kidneys alone.
From Result to Action
A confirmed A2 or A3 result does not stand alone — it is read alongside eGFR on the KDIGO heat map to set an overall risk level and a follow-up plan. Lifestyle measures, blood pressure control, and specific kidney-protective medications can lower albuminuria over time, and a falling uACR on repeat testing is a sign treatment is working. Always interpret a uACR, and any change in it, together with a clinician rather than in isolation.
uACR vs the Older Albumin Tests
Earlier approaches measured albumin alone in a single sample or required a full 24-hour collection. Measuring albumin by itself is unreliable because a concentrated or dilute sample skews the result; the 24-hour collection is accurate but burdensome and error-prone. Pairing albumin with creatinine in one spot sample solved both problems, which is why guidelines now favor uACR for both screening and monitoring. A spot uACR in mg/g also approximates the milligrams of albumin lost per day, giving a number that is easy to track over time.
Putting the Number in Context
A uACR is most informative as a trend rather than a snapshot. A value drifting upward across several visits signals progression even while each individual reading looks unremarkable, and a value falling after treatment is a sign the kidneys are being protected. Reading the ratio alongside blood pressure, blood sugar control, and eGFR turns a single lab figure into a meaningful picture of kidney health over time, which is the point of measuring it. Two people with an identical eGFR but uACR readings of 10 mg/g and 400 mg/g face very different futures, and only the albumin ratio reveals that difference.
Why Creatinine Is the Denominator
Pairing albumin with creatinine works because creatinine is excreted at a fairly steady rate, so it acts as a built-in marker of how concentrated or dilute the urine sample is. Dividing albumin by creatinine cancels out that variation: a sample taken when the patient is well hydrated and one taken when they are dry give a similar ratio even though the raw albumin concentration differs. That is the same normalising trick used in the protein/creatinine ratio, and it is what makes a single spot collection trustworthy.