Urine albumin to creatinine ratio
The urine albumin to creatinine ratio estimates albumin lost in urine. KDIGO classes below 30 mg/g as normal to mildly increased, 30 to 300 as moderately increased and above 300 as severely increased. Death and kidney failure rose with the ratio, with no threshold. One person's results varied about 30% between samples.
- Status
- A urine test ordered by a clinician, calculated from albumin and creatinine measured in the same urine sample. FDA classifies albumin immunological test systems and creatinine test systems as class II devices [1][2].
- Measures
- The amount of the protein albumin in a urine sample divided by the amount of creatinine in the same sample, which estimates how much albumin passes into the urine over 24 hours [3].
- Also called
- UACR, ACR, urine albumin-creatinine ratio, albumin/creatinine ratio, albumin creatinine ratio urine, microalbumin/creatinine ratio, urine microalbumin, microalbumin random urine, spot urine albumin, albuminuria
- Tested for
- kidney damage, chronic kidney disease staging, diabetic kidney disease, high blood pressure checkup, protein in the urine, heart risk, monitoring kidney treatment
Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on
Linked in research4
- StrongLinked to more deaths at higher ratios with no threshold, 63% more at about 30 mg/g than at about 5 mg/g across 105,872 people.
- ModerateLinked to kidney failure, with a 30% fall in the ratio over 2 years tied to 17% lower risk of end-stage kidney disease across 28 cohorts.
- ModerateShown across 41 trial comparisons that treatments lowering albuminuria by 30% went with 27% fewer kidney endpoints, less certain when starting albuminuria was low.
- LimitedOne cohort of 1,568 adults without diabetes or high blood pressure linked ratios above the group's median, far below 30 mg/g, to nearly three times the cardiovascular events.
Reported risks0
No risks sourced yet.
Reference ranges
Each range is the one its source published, in mg/g. Also reported in mg/mmol. Where sources differ, each is shown.
Kidney Disease: Improving Global Outcomes (KDIGO) guideline, 2024
Adults, as categories of albuminuria that has persisted for at least 3 months · [4], [5]
| Range | What the source calls it |
|---|---|
| below 30 mg/g | "A1 Normal to mildly increased" |
| 30 to 300 mg/g | "A2 Moderately increased" |
| above 300 mg/g | "A3 Severely increased" A doctor, immediately |
KDIGO builds these categories for albuminuria that persists, with chronic kidney disease defined by abnormalities present for a minimum of 3 months. One result does not place a person in a category: the guideline asks for a ratio of 30 mg/g or more on a random sample to be confirmed with a first morning sample. It describes A2 as moderately increased relative to the young adult level. The cut points are printed as below 30, 30 to 300 and above 300 mg/g in the guideline's nomenclature and tables, and as below 30, 30 to 299 and 300 or more in one of its figures. The factor of 0.113 to mg/mmol comes from the guideline's conversion table, and it describes its mg/mmol categories, below 3, 3 to 30 and above 30, as approximate equivalents. The categories are set for prognosis and are read together with the GFR category. The guideline's risk tables split A1 further and treat a ratio below 10 mg/g as the lowest grade of albuminuria, and a pooled analysis found more deaths at 10 mg/g than at about 5 mg/g, so the A1 band is not a level without added risk [4][5]. The guideline states that results may differ by more than 40% between laboratories depending on the method, because urine albumin measurement is not yet traceable to an international standard [4].
Kidney Disease: Improving Global Outcomes (KDIGO) guideline, 2024, children over 2 years
Children older than 2 years, on a first morning urine sample · [4]
| Range | What the source calls it |
|---|---|
| below 30 mg/g | "usually considered normal" |
| 30 or above mg/g | No name given |
The guideline states that for children over 2 years a first morning urine ratio below 30 mg/g is usually considered normal, and it names a ratio of 30 mg/g or more, confirmed on a repeat first morning sample, as a circumstance for referral to specialist kidney care. It gives no ratio for younger children, in whom urine protein is higher in the first days and weeks of life. For first testing in children it prefers the protein to creatinine ratio alongside the albumin ratio, because the albumin ratio may miss protein lost through the kidney tubules. It notes that orthostatic proteinuria is estimated to affect 2% to 5% of adolescents, which is why a first morning sample is asked for [4].
National Institute of Diabetes and Digestive and Kidney Diseases, US National Institutes of Health
Adults, in the institute's patient information on kidney tests · [3], [6]
| Range | What the source calls it |
|---|---|
| 30 or below mg/g | "normal" |
| above 30 mg/g | "may be a sign of kidney disease" |
The institute places a result of exactly 30 mg/g in its normal band, where KDIGO places it in A2. It states that a provider may repeat the test one or two more times to confirm a result [3]. Its reference sheet for professionals states that albuminuria is present when the ratio is greater than 30 mg/g, and records the older terms microalbuminuria, for 30 to 300 mg/g, and macroalbuminuria, for more than 300 mg/g [6].
Mattix and colleagues, proposed sex-specific cut points, US national survey, 2002, men
Men, on a spot urine sample · [7]
| Range | What the source calls it |
|---|---|
| below 17 mg/g | No name given |
| 17 or above mg/g | "microalbuminuria" |
Printed in µg of albumin per mg of creatinine, which is the same number as mg/g. The study applied a lower cut point in men because men excrete more creatinine, which lowers the ratio at the same albumin loss. With a single cut point of 30 for both sexes, microalbuminuria was found in 6.0% of men and 9.2% of women in a nationally representative US sample. With sex-specific cut points the difference between men and women was not significant. The abstract gives no upper limit at which a higher category begins, so this block does not separate grades above the cut point. KDIGO's 2024 categories use one set of cut points for both sexes [7][4].
Mattix and colleagues, proposed sex-specific cut points, US national survey, 2002, women
Women, on a spot urine sample · [7]
| Range | What the source calls it |
|---|---|
| below 25 mg/g | No name given |
| 25 or above mg/g | "microalbuminuria" |
Printed in µg of albumin per mg of creatinine, which is the same number as mg/g. From the same analysis as the cut point for men. The abstract gives no upper limit at which a higher category begins. KDIGO's 2024 categories use one set of cut points for both sexes, and its table of sources of variation lists lower creatinine excretion in females as a reason their ratios read higher [7][4].
How it compares with the reference method
Mixed results2
Variation from one sample to the next
Small studies found the ratio varied about 30% within one person over days to weeks, so a result had to more than double to show a real rise.
The numbers and sources
- Compared with
- The same person's results on repeat urine samples over days to weeks
- Effect
- In outpatients with chronic kidney disease sampled at 3 visits within 4 weeks, within-person variation was 32.5% for the ratio in first morning samples and 29.7% in random samples. A rise had to exceed 141% or 124%, and a fall 58% or 55%, to lie outside expected variation [12]. In outpatients sampled at 9 am on consecutive days, the change needed to show a real difference with 95% certainty was 467% for ratios below 27 mg/g, 170% for ratios of 27 to 265 mg/g and 83% for ratios above 265 mg/g [13]. A kidney guideline states that the biological variation of urine albumin exceeds 60% and that, in people being monitored, a doubling of the ratio on a later test exceeds laboratory variability [4].
- Population
- 50 clinically stable outpatients with chronic kidney disease in the United States, median ratio 173 mg/g [12]. 157 clinically stable outpatients at one Australian hospital clinic [13].
- Sources
- [12], [13], [4]
- Caveats
- Both studies enrolled clinic patients, most with kidney disease. Neither states a threshold for agreement, so the result is given as numbers only. The authors of the US study write that the variability makes it difficult to tell random change from meaningful biologic change [12].
Point-of-care tests against the laboratory
Shown to detect albuminuria with 96% sensitivity for quantitative point-of-care tests and 76% for semiquantitative ones against laboratory measurement.
The numbers and sources
- Compared with
- Laboratory measurement of the urine albumin to creatinine ratio
- Effect
- In a meta-analysis of machine-read point-of-care tests, the semiquantitative test had a sensitivity of 76% (95% CI 63% to 86%) and a specificity of 93% (84% to 97%). The quantitative test had a sensitivity of 96% (78% to 99%) and a specificity of 98% (93% to 99%). The authors conclude that a negative semiquantitative result does not rule out albuminuria, and that quantitative point-of-care testing meets required performance standards [15].
- Population
- 3,356 patients in 16 studies in primary or secondary ambulatory care [15].
- Sources
- [15]
- Caveats
- Accuracy was estimated from single urine samples, while guidelines ask for albuminuria to be confirmed on repeat samples [15].
Did not match the reference method2
Random daytime sample against a 24-hour collection
One study found random daytime samples classed 22.4% of people as having microalbuminuria against 10.0% by 24-hour collection, while first morning samples gave 7.5%.
The numbers and sources
- Compared with
- Albumin excretion in three 24-hour urine collections
- Effect
- Participants each made three 24-hour collections, a first morning sample and a random spot sample. The ratio in the first morning sample agreed most closely with 24-hour albumin excretion. The prevalence of microalbuminuria was 10.0% by 24-hour collection, 7.5% by first morning ratio and 22.4% by random spot ratio. Within-person variation of the first morning ratio was 19%, similar to the 24-hour collection, and was significantly greater for the other measures [14]. A kidney guideline states a preference for the first morning sample and accepts a random sample when none is available [4].
- Population
- 241 participants in a Dutch cohort study [14].
- Sources
- [14], [4]
- Caveats
- One study of 241 people. The US national institute describes the ratio on a spot sample as an estimate of 24-hour albumin excretion that makes timed collections unnecessary [6].
Things that shift the ratio apart from kidney disease
Limited evidence: exercise, menstruation, blood in the urine and urinary infection raise the ratio, and people who excrete less creatinine read higher at the same albumin loss.
The numbers and sources
- Compared with
- Albumin excretion measured in a timed urine collection
- Effect
- A kidney guideline lists blood in the urine, menstruation, exercise and symptomatic urinary infection as causes of a falsely elevated ratio. On the creatinine side of the ratio, it lists female sex, low body weight, acute kidney injury and low protein intake as causes of low urinary creatinine and therefore a higher ratio, and male sex, high body weight and high protein intake as causes of a lower ratio. It states that all of these can lead to false detection of chronic kidney disease or its progression [4]. In a US national sample, a single cut point of 30 for both sexes classed 9.2% of women and 6.0% of men as having microalbuminuria, and female sex was independently associated with microalbuminuria (OR 1.62, 95% CI 1.29 to 2.05). The association disappeared with sex-specific cut points [7].
- Population
- A nationally representative sample of US adults [7]. Factors listed in a guideline table [4].
- Sources
- [4], [7]
- Caveats
- The guideline lists the direction of each effect without sizes. It notes that the ratio equals albumin excretion in mg a day only on the assumption that a person excretes about 1 g of creatinine a day [4].
What studies tie it to
Linked in research4
Death from any cause and cardiovascular death
Linked to more deaths at higher ratios with no threshold, 63% more at about 30 mg/g than at about 5 mg/g across 105,872 people.
The numbers and sources
- Effect
- In a meta-analysis of general population cohorts, the ratio was related to death on a continuous scale without a threshold. Against a ratio of 0.6 mg/mmol (about 5 mg/g), the adjusted hazard ratio for death from any cause was 1.20 (95% CI 1.15 to 1.26) at 1.1 mg/mmol (10 mg/g), 1.63 (1.50 to 1.77) at 3.4 mg/mmol (about 30 mg/g) and 2.22 (1.97 to 2.51) at 33.9 mg/mmol (about 300 mg/g). Findings were similar for cardiovascular death, and the ratio and estimated GFR each added risk without interaction [5]. In a later meta-analysis of 114 cohorts, higher ratios were associated with higher rates of each of 10 outcomes studied: kidney failure, death from any cause, cardiovascular death, acute kidney injury, hospitalization, coronary heart disease, stroke, heart failure, atrial fibrillation and peripheral artery disease [8].
- Population
- 105,872 participants in 14 general population cohorts with ratio measurements [5]. 9,067,753 people with albuminuria data in 114 cohorts, with a median ratio of 11 mg/g in the main population [8].
- Sources
- [5], [8]
- Caveats
- Observational, with the ratio measured once at baseline. The first meta-analysis printed its ratios in mg/mmol, and the mg/g figures other than 10 are converted here with the factor on this page [5].
Cardiovascular events at ratios below 30 mg/g
One cohort of 1,568 adults without diabetes or high blood pressure linked ratios above the group's median, far below 30 mg/g, to nearly three times the cardiovascular events.
The numbers and sources
- Effect
- Participants with a ratio at or above the sex-specific median (3.9 mg/g for men, 7.5 mg/g for women) had a hazard ratio of 2.92 (95% CI 1.57 to 5.44) for a first cardiovascular event against those below the median, and 1.75 (0.95 to 3.22) for death. The finding held when people with a ratio of 30 mg/g or more were excluded [9].
- Population
- 1,568 adults in the Framingham Offspring Study, mean age 55, free of cardiovascular disease, hypertension and diabetes, followed for a median of 6 years, with 54 first cardiovascular events [9].
- Sources
- [9]
- Caveats
- One cohort with 54 events and wide intervals. The larger pooled analyses above also found risk rising below 30 mg/g [5].
Kidney failure
Linked to kidney failure, with a 30% fall in the ratio over 2 years tied to 17% lower risk of end-stage kidney disease across 28 cohorts.
The numbers and sources
- Effect
- In an individual-level meta-analysis, a 30% decrease in the ratio over 2 years was followed by a lower risk of end-stage kidney disease (adjusted HR 0.83, 95% CI 0.74 to 0.94, and 0.78 after correction for measurement variability). The association was stronger at higher starting ratios. In people starting at 300 mg/g or higher, a 30% fall was estimated to lower the 10-year risk of end-stage kidney disease by more than 1 percentage point [10]. A kidney guideline states that in large population studies a doubling of the ratio within 2 years is associated with a 50% to 100% higher risk of progression to kidney failure [4].
- Population
- 693,816 people in 28 cohorts, 80% with diabetes, with 7,461 end-stage kidney disease events [10].
- Sources
- [10], [4]
- Caveats
- Observational. A fall in the ratio in these cohorts had many causes, and the analysis does not show that lowering the ratio by any particular means changes the outcome [10].
Kidney outcomes in trials of treatments that lowered albuminuria
Shown across 41 trial comparisons that treatments lowering albuminuria by 30% went with 27% fewer kidney endpoints, less certain when starting albuminuria was low.
The numbers and sources
- Effect
- A meta-analysis related each treatment's effect on albuminuria at 6 months to its effect on a composite of end-stage kidney disease, estimated GFR below 15 mL/min per 1.73 m² or doubling of serum creatinine. Each 30% decrease in albuminuria relative to control was associated with an average 27% lower hazard of the composite (95% credible interval 5% to 45%). The association was stronger in patients with starting albuminuria above 30 mg/g [11].
- Population
- 29,979 participants in 41 treatment comparisons from randomized trials, 71% with diabetes, followed for a median of 3.4 years [11].
- Sources
- [11]
- Caveats
- A comparison across trials of different drugs, with a wide credible interval. The authors describe the association as less certain for patients with low albuminuria at baseline [11].
Sources
- US Food and Drug Administration. 21 CFR 866.5040, Albumin immunological test system. Electronic Code of Federal Regulations. https://www.ecfr.gov/current/title-21/section-866.5040
- US Food and Drug Administration. 21 CFR 862.1225, Creatinine test system. Electronic Code of Federal Regulations. https://www.ecfr.gov/current/title-21/section-862.1225
- National Institute of Diabetes and Digestive and Kidney Diseases. Chronic Kidney Disease Tests and Diagnosis. US National Institutes of Health. Last reviewed October 2016. https://www.niddk.nih.gov/health-information/kidney-disease/chronic-kidney-disease-ckd/tests-diagnosis
- Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney International. 2024. https://doi.org/10.1016/j.kint.2023.10.018
- Chronic Kidney Disease Prognosis Consortium, Matsushita K, van der Velde M, et al. Association of estimated glomerular filtration rate and albuminuria with all-cause and cardiovascular mortality in general population cohorts: a collaborative meta-analysis. The Lancet. 2010. https://doi.org/10.1016/S0140-6736(10)60674-5
- National Institute of Diabetes and Digestive and Kidney Diseases. Quick Reference on UACR and GFR. US National Institutes of Health. Last reviewed March 2012. https://www.niddk.nih.gov/health-information/professionals/advanced-search/quick-reference-uacr-gfr
- Mattix HJ, Hsu CY, Shaykevich S, Curhan G. Use of the Albumin/Creatinine Ratio to Detect Microalbuminuria: Implications of Sex and Race. Journal of the American Society of Nephrology. 2002. https://doi.org/10.1681/ASN.V1341034
- Writing Group for the CKD Prognosis Consortium, Grams ME, Coresh J, et al. Estimated Glomerular Filtration Rate, Albuminuria, and Adverse Outcomes: An Individual-Participant Data Meta-Analysis. JAMA. 2023. https://doi.org/10.1001/jama.2023.17002
- Ärnlöv J, Evans JC, Meigs JB, et al. Low-Grade Albuminuria and Incidence of Cardiovascular Disease Events in Nonhypertensive and Nondiabetic Individuals: The Framingham Heart Study. Circulation. 2005. https://doi.org/10.1161/CIRCULATIONAHA.105.538132
- Coresh J, Heerspink HJL, Sang Y, et al. Change in albuminuria and subsequent risk of end-stage kidney disease: an individual participant-level consortium meta-analysis of observational studies. The Lancet Diabetes and Endocrinology. 2019. https://doi.org/10.1016/S2213-8587(18)30313-9
- Heerspink HJL, Greene T, Tighiouart H, et al. Change in albuminuria as a surrogate endpoint for progression of kidney disease: a meta-analysis of treatment effects in randomised clinical trials. The Lancet Diabetes and Endocrinology. 2019. https://doi.org/10.1016/S2213-8587(18)30314-0
- Waikar SS, Rebholz CM, Zheng Z, et al. Biological Variability of Estimated GFR and Albuminuria in CKD. American Journal of Kidney Diseases. 2018. https://doi.org/10.1053/j.ajkd.2018.04.023
- Naresh CN, Hayen A, Weening A, et al. Day-to-Day Variability in Spot Urine Albumin-Creatinine Ratio. American Journal of Kidney Diseases. 2013. https://doi.org/10.1053/j.ajkd.2013.06.016
- Witte EC, Lambers Heerspink HJ, de Zeeuw D, et al. First Morning Voids Are More Reliable Than Spot Urine Samples to Assess Microalbuminuria. Journal of the American Society of Nephrology. 2009. https://doi.org/10.1681/ASN.2008030292
- McTaggart MP, Newall RG, Hirst JA, et al. Diagnostic Accuracy of Point-of-Care Tests for Detecting Albuminuria: A Systematic Review and Meta-analysis. Annals of Internal Medicine. 2014. https://doi.org/10.7326/M13-2331