What the microalbuminuria test shows
Microalbuminuria means a small amount of albumin — the main protein in blood — is leaking through the kidneys into the urine, more than normal but too little for an ordinary dipstick to detect. Healthy kidneys hold large proteins back, so even a modest leak is an early sign the glomeruli — the kidney’s filtering units — are under strain. MedlinePlus calls it one of the earliest markers of kidney damage.
It is reported as the urine albumin-to-creatinine ratio (ACR): albumin divided by creatinine in the same sample, which corrects for how dilute the urine is and lets one spot sample replace a 24-hour collection. A urinalysis dipstick and urine protein measure total protein and only turn positive once the leak is large — missing microalbuminuria. Blood creatinine gauges how fast the kidneys filter (eGFR), not how leaky the filter is: albumin reflects barrier integrity, creatinine the filtration rate — kidney disease is staged on both.
Microalbuminuria normal range
Albumin is reported as a ratio to creatinine — mg/g in the US, mg/mmol in Europe (1 mg/mmol ≈ 8.8 mg/g). KDIGO groups results into three categories:
| Category (KDIGO) | ACR, mg/g (= mg/mmol) | Meaning |
|---|---|---|
| A1 — normal to mildly increased | < 30 (< 3) | Normal |
| A2 — moderately increased (“microalbuminuria”) | 30–300 (3–30) | Early leak |
| A3 — severely increased (“macroalbuminuria”) | > 300 (> 30) | Overt proteinuria |
The older terms normo-, micro- and macroalbuminuria map onto A1–A3 at the same cutoffs. Because men excrete more creatinine (more muscle), the same leak gives a slightly lower ACR in men, so some labs use sex-specific thresholds (about 2.5 mg/mmol for men, 3.5 mg/mmol for women). Reference ranges depend on the lab, sex and age — read your result against your own report.
Why microalbuminuria is high
Causes of a raised albumin leak, in rough order of frequency:
- Diabetes (the leading cause). High blood sugar damages the glomeruli, and microalbuminuria is usually the first lab sign of diabetic kidney disease — so it is screened yearly with HbA1c and glucose, as StatPearls notes.
- High blood pressure. Hypertension injures the same filters, and the two often drive each other.
- Transient, non-kidney causes. Fever, a urine infection, hard exercise, dehydration, heart failure, menstrual contamination or a sugar spike can all raise albumin briefly — so one abnormal result is never enough.
- Other kidney disease: glomerulonephritis, IgA nephropathy, lupus nephritis and other chronic conditions.
- Cardiovascular risk. Even without diabetes, microalbuminuria signals blood-vessel (endothelial) damage and predicts heart attack and stroke, so it is read with LDL cholesterol.
When is it urgent? A severely increased result (A3, over 300 mg/g), a fast-rising ratio, or albuminuria with swelling (edema), blood in the urine or a falling eGFR needs prompt nephrology review. In pregnancy, new protein with high blood pressure can mean pre-eclampsia — an emergency.
Why microalbuminuria is low
For most tests “low” signals a problem, but for urine albumin a low or undetectable result (ACR under 30 mg/g, 3 mg/mmol) is exactly what you want — the filters are holding proteins back normally. There is no “too little” albumin in urine; treatment aims to keep it low or push a raised value down, so a falling ACR on treatment is a good sign, not a problem.
Two caveats keep a normal result honest. Early leaks can come and go, so one clear test doesn’t fully rule out kidney disease and screening is repeated over time. And albumin-specific tests miss non-albumin protein: overflow proteins such as the light chains of multiple myeloma, or tubular low-molecular-weight proteins, are not albumin, so ACR can read normal while total urine protein or electrophoresis is abnormal.
What to test alongside
Microalbuminuria is read next to markers of kidney function and its main drivers:
- Urinalysis — dipstick screen for blood, glucose and larger protein leaks.
- Urine protein — total protein, for larger or non-albumin leaks.
- Urine culture — rules out a urine infection as a transient cause.
- Creatinine — blood creatinine; the basis of eGFR (filtration rate — the second staging axis) and the ratio’s denominator.
- Urea — blood urea nitrogen (BUN); another marker of kidney function.
- HbA1c and glucose — diabetes, the commonest cause.
- LDL cholesterol and total cholesterol — cardiovascular risk that travels with albuminuria.
What to do about an abnormal result
- Don’t panic over one result, and don’t self-treat. A single raised ACR is common and often transient.
- Confirm it. Guidelines call for two of three positive samples over 3–6 months, ideally a first-morning sample taken when you are well — not after exercise, a fever, an infection or a period. NICE treats a confirmed ACR of 3 mg/mmol or more as clinically important.
- Find and treat the driver. Your doctor checks blood sugar, blood pressure and eGFR, and tightens control of diabetes and hypertension — the two biggest causes.
- Ask about kidney-protective medicines. ACE inhibitors, ARBs and, increasingly, SGLT2 inhibitors lower albuminuria and slow kidney decline in both diabetic and non-diabetic disease, per KDIGO — on prescription, with monitoring.
- See your GP or primary-care physician first. They coordinate testing and refer to a nephrologist if the ratio is severely raised (A3), rising, with a falling eGFR or blood in the urine, or the cause is unclear.
Mini-FAQ
What is microalbuminuria, and what does ACR mean?
Microalbuminuria is a small amount of albumin — a blood protein — leaking into urine, more than normal but too little for a standard dipstick to catch. It is reported as the urine albumin-to-creatinine ratio (ACR), which divides albumin by creatinine to correct for how dilute the sample is.
What ACR level is normal, and what counts as microalbuminuria?
An ACR under 30 mg/g (under 3 mg/mmol) is normal. From 30 to 300 mg/g (3–30 mg/mmol) is microalbuminuria, now called moderately increased albuminuria; above 300 mg/g is overt, severely increased albuminuria.
Does microalbuminuria mean I have kidney disease?
Not from one test. It is an early warning, most often from diabetes or high blood pressure, but fever, exercise, a urine infection or menstruation can raise albumin temporarily — so it must be confirmed on repeat samples before it counts as persistent.
Can microalbuminuria be reversed?
Often yes, especially when caught early. Controlling blood sugar and blood pressure, plus doctor-prescribed ACE inhibitors, ARBs or SGLT2 inhibitors, can lower albumin and protect the kidneys — a falling ACR is a good sign.
How is ACR different from a urine dipstick or protein test?
A standard dipstick only detects larger amounts of protein and misses the small albumin leak of microalbuminuria. ACR measures albumin specifically and is far more sensitive — the preferred early test for kidney damage in diabetes or high blood pressure.
