Protein in the urine, called proteinuria, is one of the results most often flagged on a urinalysis. On a urine dipstick, it appears as a protein grade from trace to 3+. A separate test reports urine albumin as a number called the urine albumin-to-creatinine ratio, or ACR. Canadian reports often print this result simply as “ACR,” and some reports still call it “microalbumin.”
This article explains what protein and albumin in the urine mean and how a dipstick protein result differs from an ACR or protein-to-creatinine ratio. It also explains why one abnormal result is usually repeated, and how urine albumin and eGFR are read together to check kidney health.
The reference range that applies to your result is the one printed on your laboratory report, not the typical ranges shown here. Reference ranges vary between laboratories based on the equipment used, the population tested, and individual factors such as age, sex, and pregnancy status. Always compare your result to the reference range printed on your own report, and discuss any abnormal (or unexpectedly normal) result with your doctor.
Urine protein and albumin tests measure how much protein is leaking from the blood into the urine. Healthy kidneys filter blood through millions of tiny filters called glomeruli, and these filters keep almost all protein in the blood. Albumin is the main protein in blood, and it is usually the first protein to leak when the filters are damaged. Urine albumin is a different test from the albumin blood test, which measures how much albumin is in the blood itself. Three tests are used to look for it:
A urine dipstick only begins to detect albumin once it reaches a fairly high concentration, roughly 10 to 30 mg/dL. In the earliest stage of kidney damage, the kidneys leak much less albumin than that, so a dipstick can read negative even when the kidneys have started to leak. In one large community study, only about 6 in 10 people with a dipstick reading of 1+ or higher had ACR showing increased albumin.
The dipstick also measures concentration, not total amount, so it is easily fooled by how much you have been drinking. Concentrated morning urine can produce a trace reading with no real leak, while very dilute urine can hide a small leak. For this reason, a trace protein result on its own is often not significant.
The ACR solves both problems. It measures albumin with a far more sensitive test and divides albumin by the amount of creatinine in the same sample. Creatinine is a waste product that passes into urine at a fairly steady rate, so dividing by it corrects for how concentrated or dilute the urine was. This is why the ACR, rather than the dipstick, is used to screen for early kidney damage in people with diabetes or high blood pressure.
A urine protein or ACR test needs only a single urine sample collected in a clean cup, with no special preparation. Many laboratories prefer the first urine of the morning for an ACR, because it gives the most consistent result from one test to the next. A 24-hour urine collection, where all urine is saved for a full day, is now used much less often because the ACR and PCR give similar information from one sample.
Urine protein and ACR results are read differently, depending on which test was done. A dipstick protein result is reported as a grade, and the approximate amount each grade represents is shown below:
ACR results are grouped into three categories, A1 to A3, as set out in the 2024 guideline from the International Society of Nephrology (ISN) and the Kidney Disease: Improving Global Outcomes (KDIGO). Reports in the United States usually give ACR in mg/g, while Canadian and many other reports use mg/mmol.
A PCR result uses matching categories at higher numbers because it counts all protein, not just albumin. A PCR below 150 mg/g (below 15 mg/mmol) matches A1, and a PCR of 150 to 500 mg/g (15 to 50 mg/mmol) matches A2. A PCR above 500 mg/g (above 50 mg/mmol) matches A3.
Protein or albumin in the urine has two broad categories of causes, and distinguishing between them is why a result is usually repeated.
Urine protein and albumin levels change from day to day, so one abnormal ACR or dipstick result is not enough to diagnose kidney disease. Most doctors repeat the test, often more than once over the following weeks to months, before drawing any conclusion. Under the KDIGO 2024 guideline, increased albuminuria counts as chronic kidney disease only when the ACR stays at 30 mg/g (3 mg/mmol) or higher for at least three months.
Urine albumin and the blood test eGFR measure two different things about kidney health, and doctors read them together. eGFR shows how well the kidneys filter, while ACR shows whether the filters are leaking. Chronic kidney disease can be present with a normal eGFR if the ACR stays high. At any eGFR, a higher ACR is linked to a higher chance of kidney disease getting worse over time. Our article on kidney function tests explains eGFR.
What happens after an abnormal urine protein or ACR result depends on the result’s level and whether it persists. A single trace or 1+ dipstick result usually prompts a repeat urinalysis or an ACR. A persistently increased ACR usually leads to blood tests of kidney function and a closer look at blood pressure and blood sugar. Current guidelines describe several groups of medicines that reduce albumin leakage and protect the kidneys, and your care team decides whether any of them apply to you. Very high or unexplained protein may lead to a referral to a kidney specialist (nephrologist) and, occasionally, to a kidney biopsy.