Urine Albumin/Creatinine Ratio

An ACR under 30 mg/g is normal. An ACR of 30 mg/g or more on two of three tests over 3 to 6 months means albumin is leaking into the urine. Albumin is a protein that healthy kidneys keep in the blood. Kidney guidelines count a lasting leak as chronic kidney disease, even when your eGFR looks fine ¹. ACR and eGFR answer two different questions. eGFR (estimated glomerular filtration rate) says how much filtering capacity is left. ACR says whether the filter is leaking. In diabetes, the leak often shows up before filtering drops, so ACR is frequently the first kidney number to move ³.

The ACR categories, in both units

US labs usually report ACR in milligrams of albumin per gram of creatinine (mg/g). Labs in the UK, Europe, Canada and Australia usually use milligrams per millimole (mg/mmol). KDIGO, the international kidney guideline group, sorts ACR into three categories, A1 to A3 ¹. To convert, divide mg/g by about 8.84 (see lab units explained); KDIGO rounds the cutoffs to 3 and 30 mg/mmol. You will see the word albuminuria in the table: it means albumin in the urine.

A lab flags ACR as high only from 30 mg/g, but a value of 20 mg/g is not as low-risk as a value of 5 mg/g. KDIGO's 2012 guideline split A1 into an "optimal" band below 10 mg/g and a "high normal" band of 10 to 29 mg/g ². The CKD Prognosis Consortium pooled 14 general-population cohorts with ACR data, about 106,000 people. Compared with an ACR of 5 mg/g, the risk of death was about 1.2 times higher at 10 mg/g, 1.6 times at 30 mg/g and 2.2 times at 300 mg/g, independent of eGFR ⁵. Cardiovascular deaths (from heart attack, stroke or heart failure) followed the same pattern ⁵.

Why ACR and eGFR are read together

A kidney check needs both numbers. eGFR is calculated from blood creatinine or cystatin C and falls only once a large share of filtering capacity is gone. ACR picks up damage to the filter itself, the glomeruli (the kidney's tiny filtering units), which often happens first. That is why KDIGO defines chronic kidney disease by either measure: an eGFR below 60 mL/min/1.73 m² (the unit eGFR is reported in; healthy young adults are usually around 90 to 120), or a marker of damage such as an ACR of 30 mg/g or more, lasting over 3 months ¹.

CKD is defined as abnormalities of kidney structure or function, present for a minimum of 3 months, with implications for health.KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of CKD ¹

KDIGO then places each person on a grid: an eGFR category (G1 to G5) on one axis and an ACR category (A1 to A3) on the other. Someone with an eGFR of 85 and an ACR of 150 mg/g (G2, A2) sits in a higher-risk box than someone with an eGFR of 85 and an ACR of 10 mg/g, even though their filtering estimate is the same ¹. For the full picture of how these numbers fit, see kidney function explained.

If you have an eGFR result in hand, the calculator below shows its G category so you can see where a result falls on the grid. Staging and diagnosis are done by a clinician. New to lab reports? Start with how to read any lab result and reference ranges explained.

Why a ratio beats a plain urine albumin

The albumin-to-creatinine ratio divides albumin by creatinine from the same sample, which cancels out how dilute the urine is and lets one spot sample stand in for a 24-hour collection. Creatinine, a waste product from muscle, leaves the body at a fairly steady rate. Most people excrete roughly 1 g of creatinine a day, so an ACR in mg/g roughly equals albumin excretion in mg per day ⁴. The match is looser in people with very low or very high muscle mass, because their creatinine output differs from 1 g a day ⁴. A spot ACR of 30 mg/g lines up with the old 24-hour cutoff of 30 mg per day ². A plain urine albumin concentration in mg/L, without the urine creatinine to divide by, swings with how much you drank.

A negative or trace result on a urine protein dipstick does not rule out early kidney damage. KDIGO's 2012 guideline maps the A2 range to a dipstick reading of only trace to 1+, so a strip can look unremarkable while moderately increased albuminuria is present ². That gap is why KDIGO ranks ACR first among initial tests for protein in urine, ahead of the protein-to-creatinine ratio and the dipstick on a routine urinalysis ². On lab reports you may also see urine microalbumin. KDIGO dropped the word "microalbuminuria" in favor of "moderately increased albuminuria", but many labs kept the old test name ². A urine microalbumin reported as a ratio in mg/g is the same measurement as ACR.

One high ACR is not a diagnosis

ACR varies a lot from day to day in the same person. The American Diabetes Association (ADA) counts albuminuria as present only when 2 of 3 samples collected over 3 to 6 months are abnormal ³. Several ordinary things can raise ACR for a short time: exercise within the previous 24 hours, an infection, fever, heart failure, very high blood sugar, menstruation and very high blood pressure ³. A single reading of 40 mg/g after a long run is weak evidence; three readings of 40 mg/g over four months is a finding. The same logic applies to most lab numbers, as trends beat single readings explains.

1. 1Skip hard exercise the day beforeStrenuous exercise within 24 hours can raise urine albumin temporarily ³.
2. 2Wait out a fever, infection or periodTest when you are well and not menstruating, so a temporary rise does not get counted ³.
3. 3Use a first-morning sampleKDIGO prefers an early-morning urine sample for ACR because it is the most consistent from one test to the next ².
4. 4Repeat within 3 to 6 monthsTwo abnormal results out of three, in that window, confirm albuminuria ³.

Who should have an ACR, and how often

ACR is a separate order from a routine urinalysis, so it is often never done unless someone asks for it by name. If you have diabetes or high blood pressure and have never had one, ask your clinician whether a "urine albumin-to-creatinine ratio" can be added at your next check. If your ACR comes back under 30 mg/g, the usual next step is to repeat it at your regular yearly review. Guidelines name these groups:

If you have prediabetes or a raised HbA1c or fasting glucose, ACR is one of the numbers that shows whether blood sugar has started to affect the kidneys. See blood sugar explained for how those markers connect.

How the test works in practice

• No fasting is needed. ACR is measured on a single urine sample, usually first-morning, collected at a lab or at home in a cup the lab provides.
• The lab measures albumin and creatinine in the same sample and reports the ratio in mg/g or mg/mmol.
• ACR is ordered on its own, not bundled into a standard urinalysis. If your report shows only a dipstick protein, ACR was not done.
• A 24-hour urine collection is rarely needed now, because the spot ratio approximates it ⁴.

If albuminuria is confirmed, guidelines discuss blood pressure, blood sugar and medicines that reduce albumin leakage as things to decide with a clinician ¹³. Useful questions to bring: Which G and A box am I in? When should we repeat ACR and eGFR? Are my blood pressure and blood sugar where they should be for my kidneys? To see what each grid box means, read the chronic kidney disease page. More urine markers are on the urine topic page and kidney markers on the kidney topic page.

This page is general education about lab results, not medical advice or a diagnosis. Decisions about testing and treatment belong with your clinician.

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