The urine albumin-to-creatinine ratio (uACR, often shortened to ACR) estimates albuminuria from a single spot urine sample. US laboratories report it in mg/g, and UK and other SI laboratories report it in mg/mmol. To convert, divide mg/g by 8.84. It is one of the two axes, alongside eGFR, that the KDIGO framework uses to stage chronic kidney disease and predict its risk.
How to Use This UACR Calculator
- Enter the urine albumin from the report in mg/L.
- Enter the urine creatinine and pick its unit: mg/dL (US reports) or mmol/L (UK and SI reports). A value in g/L converts to mg/dL by multiplying by 100, so 0.9 g/L is 90 mg/dL.
- Read the ACR in both mg/g and mg/mmol, with the KDIGO category (A1, A2 or A3). The category is read in the unit system you entered, so a UK result is compared with the mg/mmol cutoffs.
What the Albumin/Creatinine Ratio Is
Healthy kidneys keep albumin, a large blood protein, out of the urine. When the filtering units are damaged, small amounts leak through (albuminuria), often years before other signs appear. Measuring albumin alone in a spot sample is unreliable because urine concentration swings with hydration. Dividing by creatinine, which is excreted at a steady rate, cancels that out:
uACR (mg/g) = urine albumin (mg/L) ÷ urine creatinine (g/L)
The result is milligrams of albumin per gram of creatinine. That figure approximates 24-hour albumin excretion without the inconvenience of a timed urine collection.
Worked Example
A spot urine reports albumin of 45 mg/L and creatinine of 0.9 g/L. Divide: 45 ÷ 0.9 = 50 mg/g. That value sits in the A2 band (30 to 300 mg/g), which is moderately increased albuminuria. If a repeat first-morning sample confirms it, the result marks early kidney damage that deserves follow-up alongside the patient's eGFR. In the calculator, enter albumin 45 mg/L and creatinine 90 mg/dL.
The same sample on a UK report shows creatinine in mmol/L, and 0.9 g/L is about 7.96 mmol/L. With creatinine in mmol/L, the ratio comes out directly in mg/mmol: 45 ÷ 7.96 ≈ 5.7 mg/mmol (50 mg/g ÷ 8.84 = 5.66). That is still A2, which runs from 3 to 30 mg/mmol.
ACR Units: mg/g vs mg/mmol
Both units describe the same ratio; only the way urine creatinine is counted differs. In mg/g, creatinine is measured by mass (grams). In mg/mmol, it is counted in millimoles. One gram of creatinine is about 8.84 mmol, so:
- ACR (mg/mmol) = ACR (mg/g) ÷ 8.84
- ACR (mg/g) = ACR (mg/mmol) × 8.84
- With albumin in mg/L and creatinine in mmol/L, ACR (mg/mmol) = albumin ÷ creatinine, with no other factor needed.
The KDIGO cutoffs are published in both units as approximate equivalents: 30 mg/g sits beside 3 mg/mmol and 300 mg/g beside 30 mg/mmol. They are not exact conversions of each other (30 mg/g ÷ 8.84 is 3.39 mg/mmol). So a result of 3.0 to 3.4 mg/mmol is A2 on a UK report, while its mg/g equivalent (about 27 to 30 mg/g) is under 30. This calculator therefore reads the category in the unit you entered. When you compare results across laboratories, compare like with like and note which unit each report used.
KDIGO Albuminuria Categories
| Category | ACR (mg/g) | ACR (mg/mmol) | Description |
|---|---|---|---|
| A1 | < 30 | < 3 | Normal to mildly increased |
| A2 | 30 to 300 | 3 to 30 | Moderately increased (formerly microalbuminuria) |
| A3 | > 300 | > 30 | Severely increased (formerly macroalbuminuria) |
These bands feed the KDIGO "heat map," which combines the albuminuria category (A1 to A3) with the GFR category (G1 to G5) to grade overall kidney risk from green to red. A higher uACR shifts a patient toward the higher-risk corner of that grid independent of eGFR.
Tracking uACR Over Time
A single uACR places a patient on the KDIGO grid, but the trend over months is more useful. In diabetic and hypertensive kidney disease, treatments that lower blood pressure and block the renin-angiotensin system are expected to bring albuminuria down, and a falling uACR is taken as evidence the kidney is responding. A ratio that keeps climbing despite treatment signals progression and prompts a change in plan. For this reason uACR is rechecked at regular intervals rather than measured once. Each value is interpreted against the patient's own earlier results as well as the standard A1 to A3 bands.
Clinical Uses
uACR is the preferred test to screen for and monitor kidney damage in people with diabetes, hypertension, or established chronic kidney disease. Because albuminuria also predicts cardiovascular events, the ratio matters beyond the kidney. It is checked at diagnosis and then tracked over time, since a falling uACR on treatment is a favourable sign. Pair it with the eGFR calculator to place a patient on both KDIGO axes.
How uACR and eGFR Work Together
Kidney disease is not captured by filtration alone. Two patients can share an identical eGFR of 55 mL/min/1.73m² yet carry very different risk. The one with a uACR of 15 mg/g (A1) is at far lower risk than the one with a uACR of 450 mg/g (A3). That is why KDIGO grades risk on both axes at once. eGFR answers "how much filtering capacity remains?" while uACR answers "how leaky is the filter?" Albuminuria often appears before eGFR falls, so a rising uACR can be the earliest objective sign that the kidneys are under strain. That early signal is particularly useful in diabetes, where catching damage early changes management.
The Two-Axis KDIGO Grid
| GFR category | A1 (< 30 mg/g, < 3 mg/mmol) | A2 (30 to 300 mg/g, 3 to 30 mg/mmol) | A3 (> 300 mg/g, > 30 mg/mmol) |
|---|---|---|---|
| G1 to G2 (≥ 60) | Lowest risk | Moderate risk | High risk |
| G3a to G3b (30 to 59) | Moderate to high risk | High risk | Very high risk |
| G4 to G5 (< 30) | Very high risk | Very high risk | Very high risk |
Moving rightward across the albuminuria categories raises risk just as moving downward across the GFR categories does. A single uACR value, placed on this grid alongside eGFR, sets the colour of a patient's risk and the intensity of follow-up.
Why uACR Beats a Dipstick
A routine urine dipstick can flag protein, but it is a crude screen. It detects albumin only once it is fairly abundant, it reports concentration rather than a true rate, and it misses the low-level albuminuria that matters most for early detection. The uACR is quantitative and corrected for urine concentration, so it picks up moderately increased albuminuria (A2) that a dipstick would call negative. For populations at risk (diabetes and hypertension above all), guidelines recommend a uACR rather than a dipstick because catching that early, treatable window changes outcomes. A negative dipstick should never be taken as reassurance in a high-risk patient when a uACR has not been done.
Collecting a Reliable Sample
Because the ratio depends on a spot sample, how the sample is taken affects the result. A first-morning void is preferred: it minimises the rise in albumin that comes with daytime activity and upright posture. Vigorous exercise in the preceding 24 hours, a urinary tract infection, fever, menstrual blood, and very high protein intake can all push a result up transiently. For these reasons, an abnormal uACR is not acted on from a single sample. KDIGO advises confirming it with one or two repeat first-morning samples over weeks before assigning a category. Persistent albuminuria, confirmed this way, is what carries prognostic weight.
Limitations and Edge Cases
- A single abnormal result needs confirmation: exercise, fever, urinary infection, menstrual blood, or a high-protein meal can transiently raise it.
- A first-morning void is preferred over a random sample to reduce the effect of upright posture and activity.
- Very high or very low muscle mass alters urine creatinine and can skew the ratio in either direction.
- uACR measures albumin specifically; for total protein use the protein/creatinine ratio instead.
Read more on the albumin/creatinine ratio and the KDIGO risk heat map.