Calculate your urine albumin-to-creatinine ratio and get KDIGO 2024 kidney health classification
The Albumin-to-Creatinine Ratio (ACR) calculator is a clinical tool used by healthcare providers and patients to assess kidney health by measuring the concentration of albumin protein in the urine relative to creatinine. A single urine ACR test has been shown to be as accurate as a 24-hour urine albumin collection per National Kidney Foundation guidelines, making it the preferred screening method for chronic kidney disease (CKD) and diabetic nephropathy. Albumin is a large protein that healthy kidneys normally filter out and prevent from passing into the urine. When the kidney's filtering units — called glomeruli — are damaged or inflamed, albumin leaks into the urine. Even small elevations in urinary albumin, detectable through the ACR test, can signal early kidney damage years before kidney function declines on other tests like eGFR. This early detection window is crucial because kidney disease is largely silent in its early stages and progresses slowly, giving patients and providers the opportunity to intervene with lifestyle changes and medications to slow or halt progression. This calculator supports all major clinical unit systems, including milligrams per deciliter (mg/dL), milligrams per liter (mg/L), micrograms per milliliter (mcg/mL), micromoles per liter (µmol/L), and grams per deciliter (g/dL) for albumin. Creatinine can be entered in mg/dL, g/dL, millimoles per liter (mmol/L), or micromoles per liter (µmol/L). The calculator automatically converts all values to the standard reference units before computing the ACR in both mg/g (used in the United States) and mg/mmol (used internationally). Results are classified according to the KDIGO 2024 Clinical Practice Guideline for Chronic Kidney Disease. Category A1 (less than 30 mg/g or less than 3 mg/mmol) represents normal to mildly increased albuminuria. Category A2 (30 to 300 mg/g or 3 to 30 mg/mmol) represents moderately increased albuminuria, often called microalbuminuria, which is an early marker of kidney damage. Category A3 (greater than 300 mg/g or greater than 30 mg/mmol) represents severely increased albuminuria or macroalbuminuria, indicating significant kidney damage requiring prompt evaluation. Values exceeding 2,200 mg/g are flagged as being in the nephrotic range, a threshold that often warrants urgent specialist referral. When an estimated glomerular filtration rate (eGFR) is entered alongside the ACR, this calculator generates the full KDIGO CKD prognosis heat map — a 5-by-3 grid that cross-references the five GFR stages (G1 through G5) with the three albuminuria categories (A1 through A3) to produce a combined risk classification of Low, Moderately Increased, High, or Very High risk for CKD progression and cardiovascular events. Annual ACR screening is recommended by KDIGO, the American Diabetes Association, and the National Kidney Foundation for individuals with diabetes (Type 1 or 2), hypertension (high blood pressure), cardiovascular disease, heart failure, a family history of kidney disease, BMI over 30, tobacco use, or age over 60. The ACR can detect early kidney damage even when eGFR remains in the normal range, making it a uniquely sensitive screening marker. An important clinical note: a single abnormal ACR result should be confirmed with a repeat test within 3 to 6 months before a diagnosis of CKD is made. Transient elevations can be caused by urinary tract infection, fever, vigorous exercise, dehydration, heart failure, or poorly controlled blood pressure. KDIGO guidelines require two abnormal results over a three- to six-month period to confirm persistent albuminuria. This tool provides calculations for educational and informational purposes. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider to interpret your ACR results in the context of your full clinical picture.
Understanding Albumin-to-Creatinine Ratio
The ACR is the ratio of albumin concentration to creatinine concentration in a urine sample. It corrects for urine dilution, making a spot urine sample as reliable as timed collections.
What Is Albumin in Urine?
Albumin is the most abundant protein in blood plasma. Healthy kidneys retain albumin in the bloodstream because the glomerular filtration barrier — consisting of podocytes, a basement membrane, and endothelial cells — is designed to block large molecules like albumin from passing into the urine filtrate. When this barrier is damaged by diabetes, high blood pressure, inflammation, or other conditions, albumin leaks through into the urine. Measuring this leak provides a direct window into glomerular health. Even microalbuminuria — small amounts in the range of 30 to 300 mg/g — that are too low to be detected by routine urine dipsticks can be picked up by the ACR test, enabling detection of kidney damage at a stage when it may still be reversible or substantially delayed.
Why Is Creatinine Used as the Reference?
Creatinine is a metabolic waste product produced at a relatively constant rate by muscle tissue and excreted exclusively by the kidneys. Because its urinary concentration varies predictably with overall urine dilution, using the ratio of albumin to creatinine cancels out the effect of how concentrated or diluted the urine sample is. This means a single random urine sample taken at any time of day produces ACR results comparable to a 24-hour urine collection — which requires the patient to collect all urine over a full day and is logistically challenging. The NKF endorses spot ACR testing as the standard of care for this reason. The creatinine-based correction also makes serial monitoring more consistent across samples taken at different times of day or in different hydration states.
KDIGO Albuminuria Categories
The Kidney Disease: Improving Global Outcomes (KDIGO) organization publishes international clinical practice guidelines for kidney disease. Their 2024 guidelines classify albuminuria into three stages: A1 — normal to mildly increased, defined as an ACR below 30 mg/g (below 3 mg/mmol), which includes the healthy adult reference range of below 10 mg/g; A2 — moderately increased albuminuria (microalbuminuria), defined as 30 to 300 mg/g (3 to 30 mg/mmol), indicating early glomerular damage or impaired tubular reabsorption; and A3 — severely increased albuminuria (macroalbuminuria or proteinuria), defined as above 300 mg/g (above 30 mg/mmol), indicating more advanced kidney damage. A nephrotic threshold of 2,200 mg/g (220 mg/mmol) marks a clinically severe level of protein loss that can cause edema, low albumin blood levels, and elevated cholesterol, typically requiring specialist evaluation.
Limitations and Clinical Context
The ACR is a useful screening and monitoring tool, but several factors can cause transient or false elevations that do not reflect true kidney damage. These include urinary tract infection, fever, vigorous exercise within the past 24 hours, uncontrolled hypertension, dehydration, heart failure exacerbation, and menstrual contamination in women. For this reason, KDIGO guidelines require at least two abnormal ACR results obtained at least three months apart to confirm persistent albuminuria before diagnosing CKD. A single elevated result should prompt a repeat test. Additionally, the ACR does not replace eGFR; it is complementary to it. CKD staging uses both values together. The ACR can be elevated when eGFR is still normal (early glomerular damage) and eGFR can be reduced when ACR is still normal (tubular disease). Both measurements together provide a more complete picture of kidney health.
ACR Formulas & Equations
Albumin-to-Creatinine Ratio (mg/g)
ACR (mg/g) = Urine Albumin (mg/dL) ÷ Urine Creatinine (g/dL)
The primary ACR formula used in the United States. Divides the albumin concentration by the creatinine concentration after converting both to compatible units, yielding a ratio in milligrams of albumin per gram of creatinine.
ACR Unit Conversion (mg/mmol)
ACR (mg/mmol) = ACR (mg/g) ÷ 8.84
Converts the US-standard ACR in mg/g to the international standard in mg/mmol. The conversion factor 8.84 is derived from the molecular weight of creatinine (113.12 g/mol). This unit is used in KDIGO guidelines and most non-US laboratories.
24-Hour Albumin Excretion Estimate
24h Albumin (mg/day) ≈ ACR (mg/g) × 1.0
A spot urine ACR in mg/g approximates the 24-hour urine albumin excretion in mg/day. This equivalence has been validated by the National Kidney Foundation, making spot ACR testing the preferred screening method over timed urine collections.
Creatinine Unit Conversion
Creatinine (mg/dL) = Creatinine (µmol/L) ÷ 88.42
Converts creatinine from µmol/L (SI units used internationally) to mg/dL (conventional units used in the US). The factor 88.42 is derived from the molecular weight of creatinine and the volume conversion from liters to deciliters.
ACR Reference Tables
KDIGO Albuminuria Categories
The Kidney Disease: Improving Global Outcomes (KDIGO) 2024 classification of albuminuria into three categories based on urine albumin-to-creatinine ratio, used worldwide for CKD staging and risk assessment.
| Category | ACR (mg/g) | ACR (mg/mmol) | Clinical Term | Clinical Significance |
|---|---|---|---|---|
| A1 | <30 | <3 | Normal to mildly increased | Normal kidney function; annual monitoring if risk factors present |
| A2 | 30–300 | 3–30 | Moderately increased (microalbuminuria) | Early kidney damage; increased CKD and cardiovascular risk |
| A3 | >300 | >30 | Severely increased (macroalbuminuria) | Significant kidney damage; nephrology referral recommended |
| Nephrotic | >2,200 | >220 | Nephrotic range | Severe protein loss; urgent specialist evaluation required |
ACR vs 24-Hour Urine Albumin Equivalence
Approximate correspondence between spot urine ACR values and traditional 24-hour urine albumin excretion rates, demonstrating why spot ACR has replaced timed collections as the standard of care.
| ACR (mg/g) | 24h Albumin (mg/day) | KDIGO Category | Clinical Action |
|---|---|---|---|
| <10 | <10 | A1 (optimal) | No action; routine screening per risk factors |
| 10–29 | 10–29 | A1 (high-normal) | Monitor annually if diabetes or hypertension present |
| 30–300 | 30–300 | A2 | Confirm with repeat test; initiate ACEi/ARB if confirmed |
| >300 | >300 | A3 | Nephrology referral; optimize BP and glucose control |
| >2,200 | >2,200 | Nephrotic | Urgent nephrology evaluation; full workup for nephrotic syndrome |
ACR Worked Examples
Spot Urine ACR from Standard Lab Values
A 58-year-old patient with type 2 diabetes has a routine spot urine test showing albumin of 4.5 mg/dL and creatinine of 150 mg/dL (1.5 g/dL).
Convert creatinine to g/dL: 150 mg/dL ÷ 1000 = 0.15 g/dL. Wait — 150 mg/dL = 150/100 = 1.5 g/L. Actually: 150 mg/dL stays as-is for the ratio, but we need g/dL: 150 mg/dL ÷ 1000 = 0.15 g/dL.
Calculate ACR in mg/g: ACR = Albumin (mg/dL) ÷ Creatinine (g/dL) = 4.5 ÷ 0.15 = 30 mg/g.
Convert to international units: ACR (mg/mmol) = 30 ÷ 8.84 = 3.4 mg/mmol.
Classify per KDIGO: ACR of 30 mg/g falls at the lower boundary of category A2 (moderately increased albuminuria / microalbuminuria).
ACR = 30 mg/g (3.4 mg/mmol), KDIGO Category A2. This result indicates early kidney damage. A repeat test in 3–6 months is needed to confirm persistent albuminuria before diagnosing CKD. If confirmed, ACE inhibitor or ARB therapy should be discussed with the provider.
High ACR with eGFR for Combined CKD Risk Staging
A 65-year-old patient with hypertension has urine albumin of 25 mg/dL and urine creatinine of 50 mg/dL. Their eGFR is 52 mL/min/1.73 m².
Convert creatinine: 50 mg/dL ÷ 1000 = 0.05 g/dL.
Calculate ACR: 25 ÷ 0.05 = 500 mg/g.
Convert: 500 ÷ 8.84 = 56.6 mg/mmol.
Classify albuminuria: ACR of 500 mg/g = KDIGO category A3 (severely increased).
Classify GFR: eGFR of 52 = KDIGO stage G3a (mildly to moderately decreased).
Combined risk: G3a + A3 = Very High risk on the KDIGO CKD prognosis heat map.
ACR = 500 mg/g (56.6 mg/mmol), KDIGO A3 + G3a = Very High CKD risk. Prompt nephrology referral is indicated. Blood pressure optimization, RAAS blockade, and SGLT-2 inhibitor therapy should be considered.
ACR from International Units (µmol/L)
A patient in the UK has urine albumin of 45 mg/L and urine creatinine of 8.8 mmol/L.
Convert albumin from mg/L to mg/dL: 45 ÷ 10 = 4.5 mg/dL.
Convert creatinine from mmol/L to mg/dL: 8.8 × 8.842 = 77.8 mg/dL, then to g/dL: 77.8 ÷ 1000 = 0.0778 g/dL.
Calculate ACR: 4.5 ÷ 0.0778 = 57.8 mg/g.
Convert to mg/mmol: 57.8 ÷ 8.84 = 6.5 mg/mmol.
Classify: ACR of 57.8 mg/g (6.5 mg/mmol) = KDIGO category A2 (moderately increased).
ACR = 57.8 mg/g (6.5 mg/mmol), KDIGO Category A2 (microalbuminuria). Repeat testing recommended to confirm. Early intervention with blood pressure control and possible RAAS blockade is warranted.
How to Use the ACR Calculator
Enter Your Urine Albumin Value
Find the albumin concentration on your urine test report. Select the matching unit from the dropdown — most US labs report in mg/dL, while international labs may use mg/L or µmol/L. The calculator automatically converts all units before computing the ratio.
Enter Your Urine Creatinine Value
Enter the creatinine concentration from the same urine sample and select the correct unit (mg/dL is most common in US labs; mmol/L or µmol/L are common in European and Australian labs). Both values must come from the same spot urine sample.
Review Your ACR and KDIGO Category
Your ACR is displayed in both mg/g (US standard) and mg/mmol (international standard), along with your KDIGO albuminuria category (A1, A2, or A3), a color-coded classification bar, and a plain-language clinical interpretation of what your result means.
Add eGFR for Full CKD Risk Staging
Expand the Advanced Options section and enter your eGFR (estimated glomerular filtration rate) if available. This generates the KDIGO 5-by-3 CKD risk heat map showing your combined Low, Moderately Increased, High, or Very High risk level across all GFR and albumin stage combinations.
Frequently Asked Questions
What is a normal ACR value?
A normal ACR is below 30 mg/g (below 3 mg/mmol), which corresponds to KDIGO albuminuria category A1 — normal to mildly increased. Healthy young adults typically show ACR values below 10 mg/g. Values between 10 and 30 mg/g are within the normal A1 range but are on the higher end, and may warrant monitoring in people with risk factors. An ACR of 30 mg/g or above signals moderately increased albuminuria (microalbuminuria, category A2), which is a sign of early kidney damage. A value above 300 mg/g indicates severely increased albuminuria (macroalbuminuria, category A3). Two confirmed abnormal results at least 3 months apart are needed to diagnose persistent albuminuria per KDIGO guidelines.
Is a spot urine ACR as accurate as a 24-hour urine test?
Yes. Research published in the British Medical Journal and endorsed by the National Kidney Foundation has demonstrated that a random spot urine ACR has equivalent diagnostic accuracy to a 24-hour urine albumin excretion measurement for detecting significant albuminuria. The creatinine correction in the ACR ratio accounts for urine dilution differences, which is what made 24-hour collections necessary in the past. Spot ACR testing is now the preferred standard of care in primary care, nephrology, endocrinology, and cardiology because it is far more convenient for patients and produces reliable results. The first morning urine sample is often preferred for slightly better consistency, but any random spot sample is clinically acceptable.
What can cause a temporarily elevated ACR that is not kidney disease?
Several factors can transiently elevate the ACR without reflecting true underlying kidney damage. The most common causes include urinary tract infection, fever or acute illness, vigorous exercise in the 24 hours before sample collection, significant dehydration, poorly controlled hypertension, decompensated heart failure, and menstrual blood contamination in women. For this reason, KDIGO guidelines require two abnormal ACR results taken at least 3 months apart to confirm persistent albuminuria before a diagnosis of CKD is made. If your first ACR is elevated, avoid strenuous exercise for 24 hours before the retest, ensure you are well-hydrated but not overhydrated, and collect the sample when you are not acutely ill or have a UTI.
How does the KDIGO heat map work and what does my combined risk mean?
The KDIGO CKD Risk Matrix is a 5-by-3 color-coded grid that combines two independent dimensions of kidney health: your GFR stage (G1 through G5, representing kidney function levels) and your albuminuria category (A1 through A3, representing kidney damage level). Low risk (green) corresponds to G1 or G2 GFR with A1 albuminuria. Moderately Increased risk (yellow) appears at G1–G2 with A2, or G3a with A1. High risk (orange) appears at G1–G2 with A3, G3a with A2, or G3b with A1. Very High risk (red) covers G3b with A2–A3, and all G4 and G5 combinations. Higher combined risk is associated with faster CKD progression and increased cardiovascular event risk. This matrix guides referral decisions and treatment intensity.
Who should get an ACR test and how often?
Annual ACR testing is recommended by KDIGO, the American Diabetes Association, and the National Kidney Foundation for all adults with diabetes (Type 1 or 2), hypertension (high blood pressure), established cardiovascular disease or heart failure, a family history of kidney disease or hereditary kidney conditions, BMI over 30, tobacco use, or age over 60. For people already diagnosed with CKD, ACR testing frequency depends on risk category: annual for Low risk, 1–2 times per year for Moderately Increased risk, 2–3 times per year for High risk, and 3 or more times per year for Very High risk. For healthy adults without risk factors, routine ACR screening is not universally recommended but may be offered at health checkups.
What treatments can reduce an elevated ACR?
The ACR can often be reduced with targeted treatment, particularly in early-stage kidney disease. Blood pressure control to a target below 130/80 mmHg using renin-angiotensin-aldosterone system (RAAS) blockers — specifically ACE inhibitors or ARBs — has strong evidence for reducing albuminuria and slowing CKD progression. In people with type 2 diabetes, SGLT-2 inhibitors (such as empagliflozin and dapagliflozin) and GLP-1 receptor agonists have demonstrated significant ACR reduction in clinical trials. Tight glycemic control in diabetes (target HbA1c below 7%) also reduces albuminuria. Dietary protein restriction, smoking cessation, and weight loss in obese patients may provide additional benefit. Always work with your nephrologist or primary care provider to determine the right treatment plan.
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Calculate estimated glomerular filtration rate (eGFR) to assess kidney function. Use alongside ACR for complete KDIGO CKD staging.
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Classify blood pressure readings and assess hypertension staging — hypertension is a leading cause of kidney damage and elevated ACR.
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