Urine Albumin-to-Creatinine Ratio (UACR): calculation, units and KDIGO categories
What the UACR measures and when it is ordered
The albumin-to-creatinine ratio (UACR) estimates urinary albumin loss with a single urine sample, without a 24-hour collection. Creatinine goes in the denominator to correct for dilution: according to the 2024 KDIGO guideline, creatinine excretion is reasonably constant throughout the day, and the ratio compensates for more concentrated or more dilute urine.
KDIGO places the UACR as the first option for initial albuminuria testing, preferably on a first morning, midstream urine. Albuminuria is one of the axes of chronic kidney disease staging, alongside glomerular filtration, which can be estimated by the CKD-EPI equation.
In Brazil, the guideline of the Brazilian Diabetes Society (SBD) recommends the UACR in a random sample to screen for diabetic kidney disease: at the diagnosis of type 2 diabetes and five years after the diagnosis of type 1. When the goal is to measure total protein, not just albumin, the alternative is the spot urine protein-to-creatinine ratio.
How to use the calculator: inputs and result
The calculator asks for two results from the same urine sample:
- Urine albumin, in mg/L, from 0 to 20,000. The unit µg/mL is equivalent, since 1 mg/L = 1 µg/mL. Example: 20.
- Urine creatinine, in mg/dL, greater than zero and up to 1,000. Example: 100.
Values outside these ranges produce an error message with the most likely unit conversion. The tool shows:
- Albumin-to-creatinine ratio, in mg/g, with one decimal place, as KDIGO 2024 recommends reporting.
- UACR in mg/mmol, using the KDIGO factor of 0.113.
- KDIGO albuminuria category: A1, normal to mildly increased; A2, moderately increased; or A3, severely increased.
The category is applied to the value with one decimal place: 30.0 mg/g already falls into A2, and 300.0 mg/g still falls into A2, as in the KDIGO table (A2 from 30 to 300 mg/g). The text reminds you that the category applies to persistent albuminuria and that a result of 30 mg/g or more should be confirmed.
UACR formula and unit conversion
The UACR is albumin divided by creatinine, with both on the same volume basis. The tool converts creatinine from mg/dL to g/L by dividing by 100, because 100 mg/dL = 1,000 mg/L = 1 g/L:
UACR (mg/g) = Albumin (mg/L) ÷ [Creatinine (mg/dL) ÷ 100]
The same calculation can be written as UACR = Albumin × 100 ÷ Creatinine. The units cancel as follows: milligrams of albumin per liter, divided by grams of creatinine per liter, give milligrams of albumin per gram of creatinine.
Other common units on reports:
- Albumin in mg/dL: multiply by 10 to obtain mg/L.
- Creatinine in µmol/L: divide by 88.4 to obtain mg/dL, the KDIGO conversion factor.
- UACR in mg/mmol: KDIGO gives mg/g × 0.113 = mg/mmol; 30 mg/g corresponds to about 3.4 mg/mmol.
Step-by-step worked example
The following example is didactic and does not represent the clinical interpretation of a patient. Consider urine albumin of 45 mg/L and urine creatinine of 150 mg/dL in the same sample.
- Creatinine in g/L: 150 ÷ 100 = 1.5 g/L.
- UACR: 45 ÷ 1.5 = 30.0 mg/g.
- Category displayed: A2, moderately increased, because 30 belongs to that range. In mg/mmol: 30 × 0.113 = 3.4.
Two other cases checked in the tool:
- Albumin 20 mg/L and creatinine 100 mg/dL: UACR of 20.0 mg/g, category A1.
- Albumin 400 mg/L and creatinine 80 mg/dL: UACR of 500.0 mg/g, category A3.
The first case shows how a borderline result changes category with very little: 44 mg/L with the same creatinine would give 29.3 mg/g. Because albuminuria varies from day to day, KDIGO asks that a UACR of 30 mg/g or more in a random sample be confirmed on a first morning urine, and the SBD asks for confirmation in 2 of 3 samples collected within 6 months.
How to understand the UACR: categories A1, A2 and A3
The 2024 KDIGO guideline classifies persistent albuminuria into three categories. The cutoffs match those used by the tool:
| Category | UACR (mg/g) | UACR (mg/mmol) | KDIGO description |
|---|---|---|---|
| A1 | below 30 | below 3 | Normal to mildly increased |
| A2 | 30 to 300 | 3 to 30 | Moderately increased |
| A3 | above 300 | above 30 | Severely increased |
The tool uses KDIGO nomenclature. Since 2012, the guideline has recommended that laboratories stop using the terms microalbuminuria and macroalbuminuria, replaced by moderately increased (A2) and severely increased (A3) albuminuria.
An isolated high UACR is not enough to classify the patient: the category applies to persistent albuminuria, and chronic kidney disease requires abnormalities for at least three months. According to the SBD guideline, fever, intense exercise, decompensated heart failure, marked hyperglycemia, symptomatic urinary tract infection and uncontrolled hypertension can raise the UACR transiently. The clinical conclusion is the responsibility of the professional.
Common errors, limitations and checklist
The most common errors in the UACR come from mixed-up units and inadequate samples. Points to check:
- Albumin in mg/dL entered as mg/L produces a UACR ten times lower.
- Creatinine in µmol/L entered as mg/dL distorts the result; convert first.
- Different samples: albumin and creatinine must come from the same urine.
- Storage: KDIGO recommends analyzing albumin in a fresh sample or one stored at 4 °C for up to 7 days, and not frozen at −20 °C.
The UACR also has biological limits, listed in Table 16 of KDIGO 2024. Women and people of low body weight excrete less creatinine, which raises the UACR; men, people of higher body weight and those on a high-protein diet tend to have a lower UACR. In acute kidney injury, lower creatinine excretion also raises the ratio. In children, KDIGO prefers a first morning urine and asks for UPCR and UACR together.
Checklist: albumin in mg/L; creatinine in mg/dL; same sample, preferably the first morning urine; no fever, intense exercise or urinary tract infection on the day; abnormal result confirmed in a new sample.
UACR, protein-to-creatinine ratio and 24-hour urine
The UACR measures only albumin, whereas total proteinuria also includes other proteins. KDIGO 2012 approximates the equivalences between methods assuming creatinine excretion of about 1 g per day:
| Category | 24-h albumin (mg/24h) | UACR (mg/g) | UPCR (mg/g) |
|---|---|---|---|
| A1 | below 30 | below 30 | below 150 |
| A2 | 30 to 300 | 30 to 300 | 150 to 500 |
| A3 | above 300 | above 300 | above 500 |
The 24-hour collection remains the reference for demonstrating urinary loss, but it is hard to control; that is why KDIGO accepts the UACR as an alternative to the timed measurement. The SBD states that 24-hour urine is not necessary to screen, diagnose and monitor diabetic kidney disease. To quantify total protein over 24 hours, use the 24-hour urine protein calculator. The dipstick ranks below the UACR in the KDIGO order of preference and, when positive, should be confirmed by a quantitative measurement. In people with diabetes, glycemic control can be followed with the estimated average glucose from HbA1c.
Frequently asked questions about the urine albumin-to-creatinine ratio (UACR)
What is the difference between UACR and microalbuminuria?
Microalbuminuria is the old name for the 30 to 300 mg/g range. KDIGO recommends calling it moderately increased albuminuria (category A2). The UACR is the test that measures this albuminuria in a spot sample.
Does the UACR need to be done on the first morning urine?
It is the sample preferred by KDIGO, midstream. A random sample is accepted, and a UACR of 30 mg/g or more in it should be confirmed on a first morning urine.
How do I convert the UACR from mg/g to mg/mmol?
Multiply by 0.113, the KDIGO factor. Thus, 30 mg/g corresponds to about 3.4 mg/mmol; the KDIGO category table uses the rounded values of 3 and 30 mg/mmol.
The albumin on my report is in mg/dL. Can I use the calculator?
Yes, after converting: multiply by 10 to obtain mg/L. For example, 4.5 mg/dL is 45 mg/L.
Does a single abnormal result confirm kidney disease?
No. The SBD asks for confirmation in 2 of 3 samples collected within 6 months, and KDIGO defines chronic kidney disease by abnormalities persisting for at least 3 months. Fever, intense exercise and urinary tract infection can raise the UACR temporarily.
References
- Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117-S314. doi:10.1016/j.kint.2023.10.018. View
- Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int Suppl. 2013;3(1):1-150. View
- Sá JR, Canani LH, Rangel EB, Bauer AC, Escott GM, Zelmanovitz T, et al. Avaliação e tratamento da doença renal do diabetes. Diretriz Oficial da Sociedade Brasileira de Diabetes. 2024. doi:10.29327/5412848.2024-6. View
Updated . A support tool for educational purposes; it does not replace clinical assessment.