A microalbumin-creatinine ratio test measures a small amount of albumin in urine and compares it with urine creatinine. The modern name is urine albumin-to-creatinine ratio, or uACR. It is one of the most useful tests for detecting early kidney damage because albumin can begin leaking into urine before a person has symptoms or a major fall in estimated glomerular filtration rate (eGFR). The test is especially important in diabetes and high blood pressure, two common causes of chronic kidney disease. A spot urine sample is usually enough, and a first-morning specimen is often preferred when an abnormal result needs confirmation. A uACR below 30 mg/g is generally A1, 30–299 mg/g is A2 or moderately increased albuminuria, and 300 mg/g or higher is A3 or severely increased albuminuria. Because albumin excretion changes from day to day, one high result usually needs repeat testing before persistent kidney damage is diagnosed.
- A microalbumin-creatinine ratio is the same basic test now called uACR; “microalbumin” refers to a small amount of albumin, not a different protein.
- uACR below 30 mg/g is A1, 30–299 mg/g is A2, and 300 mg/g or higher is A3 albuminuria.
- A random spot urine sample is acceptable for screening, while a first-morning sample can reduce variability when confirming an abnormal result.
- Exercise, fever, infection, marked hyperglycemia, menstruation, heart failure, and severe hypertension can temporarily raise uACR.
- Persistent albuminuria can signal kidney damage even when eGFR remains normal or near normal.
Table of Contents
- What the Microalbumin-Creatinine Ratio Measures
- Normal and High uACR Ranges
- Why Creatinine Is in the Ratio
- Who Needs uACR Testing
- Sample Timing, Preparation, and False High Results
- What a High Result Can Mean
- Repeat Testing and Follow-Up
What the Microalbumin-Creatinine Ratio Measures
The test measures urine albumin and urine creatinine in the same specimen, then reports albumin relative to creatinine. In the United States, the usual unit is milligrams of albumin per gram of creatinine (mg/g). Many other countries use mg/mmol.
Albumin is a major blood protein. Healthy glomeruli—the microscopic filters in the kidneys—keep most albumin in the bloodstream. When the filtration barrier is damaged or under abnormal pressure, more albumin can cross into urine. Small increases can be detected by sensitive albumin assays before a standard total-protein dipstick becomes strongly positive.
The older name “microalbumin-creatinine ratio” developed because the test was designed to detect small quantities of urinary albumin. The albumin molecule itself is not smaller. Current kidney guidelines therefore prefer the terms urine albumin-creatinine ratio and albuminuria.
uACR is a marker of kidney damage, not a direct measurement of filtration. Serum creatinine and eGFR answer the filtration question. Both are needed because kidney disease can present with albumin leakage, reduced filtration, or both.
A direct urine albumin concentration in mg/L can also be measured, but concentration changes substantially with hydration. uACR is generally more informative because it corrects partly for how dilute or concentrated the urine is.
Normal and High uACR Ranges
uACR is classified into three categories used in chronic kidney disease staging and risk assessment.
| Category | uACR in mg/g | uACR in mg/mmol | Description |
|---|---|---|---|
| A1 | <30 | <3 | Normal to mildly increased |
| A2 | 30–299 | 3–30 | Moderately increased |
| A3 | ≥300 | >30 | Severely increased |
A result below 30 mg/g is generally considered A1, but “normal” should not be understood as zero risk. Albuminuria is a continuous marker: kidney and cardiovascular risk tends to rise as uACR rises, including across values within the A1 range.
A2 corresponds to what was traditionally called microalbuminuria. A3 was often called macroalbuminuria. Modern terminology is more precise because it describes the degree of albumin increase without implying different forms of albumin.
The cutoffs should also not be treated as sharp biological boundaries. A uACR of 28 mg/g and 32 mg/g are very similar measurements. Trends, repeat results, eGFR, blood pressure, diabetes status, and other risk factors matter more than a one-time crossing of a category line.
A very low uACR is generally reassuring and is not a sign that the body lacks albumin. The concern is excess urinary albumin, not a low urine value.
Why Creatinine Is in the Ratio
Urine concentration changes throughout the day. After drinking a large amount of water, both albumin and creatinine concentrations may be lower simply because the urine is dilute. After overnight fluid restriction or dehydration, both may be higher. Dividing albumin by creatinine helps reduce this concentration effect.
Urine creatinine is produced from muscle creatine metabolism and is excreted relatively steadily within an individual. That makes it a useful denominator, but it is not perfect. Low muscle mass can reduce creatinine excretion and make uACR appear somewhat higher for the same actual albumin loss. High muscle mass can have the opposite effect.
This is why unusual body composition, frailty, amputation, very high muscularity, or other factors can complicate interpretation. In selected cases, a clinician may confirm the result with a timed 24-hour urine albumin test or repeat a first-morning specimen.
The urine creatinine in uACR should not be confused with a blood creatinine test. Serum creatinine is used to estimate GFR. Urine creatinine mainly helps normalize a spot urine measurement or assess a timed collection.
The ratio is therefore best thought of as a practical estimate of albumin excretion that avoids the inconvenience and error risk of collecting every urine sample for a full day.
Who Needs uACR Testing
uACR is most valuable in people with a meaningful risk of chronic kidney disease. Diabetes and high blood pressure are two of the main reasons the test is ordered.
Current diabetes guidance recommends uACR and eGFR at least annually for:
- all people with type 2 diabetes, beginning at diagnosis;
- people with type 1 diabetes once the duration reaches at least 5 years.
People who already have CKD are usually monitored more often, often one to four times per year depending on eGFR, albuminuria, progression risk, and whether results will change treatment.
Hypertension also increases the risk of glomerular damage and CKD. uACR helps determine whether high blood pressure is associated with kidney damage and can influence cardiovascular and renal risk assessment. Persistent albuminuria in a person with hypertension may strengthen the indication for specific kidney-protective blood pressure treatment, depending on the overall clinical picture.
Other situations in which uACR may be ordered include established cardiovascular disease, known CKD, family history of kidney disease, systemic disorders that affect the kidneys, or a positive protein finding on routine urinalysis.
The test is not a cancer screen and does not detect all forms of proteinuria. If a clinician suspects tubular proteins or monoclonal light chains, total protein, electrophoresis, immunofixation, or other specific tests may be more appropriate.
Sample Timing, Preparation, and False High Results
A random spot urine is usually acceptable, but a first-morning sample is often preferred for confirmation because it is less affected by daytime activity, posture, diet, and variable fluid intake.
Special fasting is usually not required. The most important preparation is avoiding conditions that could create a misleading temporary rise when practical. Factors known to increase uACR independently of chronic structural kidney damage include:
- strenuous exercise within about 24 hours;
- fever or acute illness;
- urinary tract or systemic infection;
- marked hyperglycemia;
- markedly elevated blood pressure;
- decompensated heart failure;
- menstruation or blood contamination.
If one of these is present, a clinician may delay testing or repeat the result later. A borderline high uACR collected immediately after a hard endurance workout should not be interpreted the same way as repeated A2 albuminuria from first-morning samples over several months.
Hydration affects urine concentration less when a ratio is used, but extreme changes can still add variability. There is no need to deliberately drink extra water before the test. A routine, representative sample is preferable.
Urinary tract infection can be particularly confusing because inflammation and blood may increase measured albumin. If symptoms such as burning, urgency, fever, or flank pain are present, infection may need to be evaluated before an albumin result is classified as chronic kidney damage.
What a High Result Can Mean
Persistent high uACR most often reflects glomerular kidney damage. Diabetes and hypertension are common causes, but the test does not identify a specific disease.
In diabetes, chronic hyperglycemia, glomerular hypertension, inflammation, and vascular changes can damage the filtration barrier. Albuminuria may rise gradually, although some people with diabetic kidney disease lose eGFR without developing A2 or A3 albuminuria.
In hypertension, prolonged pressure and vascular injury can damage glomeruli and increase albumin leakage. Albuminuria also acts as a marker of broader vascular risk, so a high result has implications beyond the kidney.
Other causes include glomerulonephritis, lupus nephritis, focal segmental glomerulosclerosis, membranous nephropathy, heart failure, obesity-related kidney disease, pregnancy-related kidney disorders, and acute kidney injury. Very heavy albuminuria can occur with nephrotic syndrome.
The result becomes more concerning when it is paired with a falling eGFR, hematuria, cellular casts, edema, or rapidly increasing protein loss. Those features can suggest more advanced or atypical disease and may justify nephrology evaluation.
A normal uACR does not exclude all kidney disease. Tubular disorders may produce non-albumin proteins, and CKD can exist with reduced eGFR despite A1 albuminuria. Kidney screening therefore requires both urine and blood assessment.
Repeat Testing and Follow-Up
Because uACR has substantial biological variability, persistence is more important than one isolated result. In diabetes care, two of three abnormal uACR samples collected over approximately 3–6 months are commonly used to confirm moderately or severely increased albuminuria.
Once albuminuria is confirmed, the clinician considers the cause and overall kidney risk. Follow-up commonly includes serum creatinine and eGFR, blood pressure, diabetes control, medication review, and urinalysis. Total urine protein may be added when protein loss is heavy or the albumin fraction seems unexpectedly small.
The albuminuria category and eGFR are used together to stage CKD and estimate progression risk. People with A3 albuminuria and reduced eGFR generally need closer monitoring than people with isolated low-level A2 albuminuria and preserved filtration.
Treatment targets the cause and the risk. Depending on the patient, this can include better blood pressure control, improved glycemic management, renin-angiotensin system blockers, SGLT2 inhibitors, nonsteroidal mineralocorticoid receptor antagonists, GLP-1 receptor agonists, or treatment for a specific glomerular disease. Medication choice depends on diagnosis, eGFR, potassium, blood pressure, diabetes type, and other clinical factors.
A sustained fall in uACR can be a favorable sign. In people with diabetes, CKD, and albuminuria at least 300 mg/g, current guidance recommends aiming for a reduction of 30% or more when feasible because this degree of albumin reduction is associated with slower kidney disease progression.
Seek prompt medical care for high urine protein accompanied by severe swelling, shortness of breath, very low urine output, visible blood in urine, rapidly worsening kidney function, or severe blood pressure elevation. A stable mildly elevated uACR usually calls for timely outpatient confirmation rather than emergency care.
Common uACR Scenarios and What They Mean
A uACR result is easier to use when it is placed into a common clinical pattern. One frequent scenario is a first result of 45 mg/g in a person with diabetes who otherwise feels well. That value is in the A2 range, but a single sample does not prove persistent albuminuria. Repeating the test—ideally with a first-morning specimen and without a temporary trigger—helps establish whether the finding represents chronic kidney damage.
Another pattern is a uACR of 400 mg/g with a normal or near-normal eGFR. The preserved filtration estimate does not cancel the urine abnormality. Persistent A3 albuminuria is itself a significant kidney-damage marker and is associated with higher kidney and cardiovascular risk. The clinician will usually confirm the result, review blood pressure and diabetes control, evaluate urinalysis, and consider kidney-protective treatment or referral depending on the full picture.
The reverse can also occur: uACR may be 10 mg/g while eGFR is persistently below 60 mL/min/1.73 m². That person can still have CKD. Albuminuria is only one dimension of kidney disease, and some diabetic, vascular, tubulointerstitial, and structural kidney disorders produce little albumin leakage.
Creatinine in the denominator deserves special attention at the extremes of muscle mass. Someone with very low muscle mass may excrete less creatinine, which can make a given amount of albumin produce a higher ratio. A highly muscular person may excrete more creatinine and have a lower ratio for the same albumin concentration. This does not make uACR unreliable for most people, but it explains why unexpected results sometimes need confirmation with repeat samples or, less commonly, a timed collection.
The urine concentration by itself is also misleading. For example, 20 mg/L of albumin in very dilute urine and 20 mg/L in concentrated urine do not carry the same implication. Dividing albumin by creatinine partially corrects for that dilution difference. This is why uACR is generally more useful than a urine albumin concentration reported without a creatinine ratio.
Finally, change over time is often more clinically useful than one threshold crossing. A shift from 35 to 40 mg/g may reflect normal variability, while a sustained rise from 40 to 250 mg/g deserves closer review even though both results remain A2. Repeated measurements under similar conditions make true trends easier to distinguish from noise.
What the Ratio Cannot Tell You by Itself
uACR does not identify the exact kidney disease. Diabetes and hypertension are common causes of albuminuria, but autoimmune glomerulonephritis, primary glomerular disease, heart failure, obesity-related kidney disease, infection, and other conditions can produce similar values. Urine microscopy, blood tests, imaging, and occasionally kidney biopsy are needed when the pattern is atypical.
It also does not quantify every urinary protein. A patient with a plasma-cell disorder or proximal tubular disease may have important non-albumin protein loss despite a modest uACR. When total protein seems disproportionately high, clinicians may add UPCR, electrophoresis, immunofixation, or low-molecular-weight protein testing. The ratio should therefore be treated as a focused albumin marker within a broader kidney assessment, not as a universal urine-protein test.
Why First-Morning Urine Is Often Preferred
A first-morning sample is convenient and tends to reduce variation from recent meals, daytime activity, and upright posture. It is not mandatory for every uACR, but it is particularly useful when confirming a borderline or unexpected abnormal result. The sample should be collected according to laboratory instructions, and contamination with menstrual blood or a urinary infection should be considered when results do not fit the clinical picture.
A random daytime sample remains acceptable for routine screening in many settings. If it is clearly abnormal, the clinician may act on the result while arranging confirmation rather than delaying evaluation. The advantage of first-morning testing is mainly improved consistency, not a different set of albuminuria categories.
How High Blood Pressure Fits Into the Result
Albuminuria and hypertension can reinforce each other. High intraglomerular pressure can increase albumin leakage, while persistent albuminuria identifies people with greater kidney and cardiovascular risk. Blood pressure should therefore be measured and interpreted alongside uACR rather than treated as a separate issue.
If uACR rises during a period of markedly uncontrolled blood pressure, improvement after blood-pressure control can help show how much of the elevation was hemodynamic. Persistent albuminuria despite better pressure control still warrants CKD risk assessment and treatment review.
References
– Executive summary of the KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease: known knowns and known unknowns 2024 (Guideline) – Urine Albumin Measurements in Clinical Diagnostics 2024 (Review) – Developments in albuminuria testing: A key biomarker for detection, prognosis and surveillance of kidney and cardiovascular disease-A practical update for clinicians 2025 (Review) – 11. Chronic Kidney Disease and Risk Management: Standards of Care in Diabetes-2026 2026 (Guideline) – Practicalities and importance of assessing urine albumin excretion in type 2 diabetes: A cutting-edge update 2024 (Review)
Disclaimer
This article provides general information about uACR testing and is not a diagnosis or treatment plan. Albumin results can vary with exercise, illness, infection, glucose, blood pressure, and sample timing, and laboratory methods may differ. Discuss persistent or markedly abnormal uACR results with a qualified healthcare professional.
