Protein in urine levels: what the dipstick grades mean, the common and serious causes, and how it is confirmed

Healthy kidneys filter about 180 liters of blood a day and keep almost all of its protein; the filter (glomerulus) blocks large proteins such as albumin, and the tubules reabsorb most of the small ones that slip through. Less than 150 mg of protein leaves in the urine each day, and less than 30 mg of that is albumin. The dipstick's protein pad changes color when albumin is present, from trace (about 15–30 mg/dL) through 1+ (30), 2+ (100), 3+ (300) to 4+ (1,000 mg/dL or more).

Because the pad reads a concentration, the same amount of protein looks worse in concentrated morning urine and better after a liter of water, and the pad is far more sensitive to albumin than to other proteins. Light-chain proteins from multiple myeloma (Bence Jones protein) are largely invisible to it, which is why a sulfosalicylic acid test or a urine protein electrophoresis is ordered when myeloma is a concern despite a negative dipstick.

The confirmatory test is the urine albumin-to-creatinine ratio (UACR) on a spot sample, which corrects for urine concentration: under 30 mg/g is normal, 30–300 mg/g is moderately increased (what used to be called microalbuminuria), and above 300 mg/g is severely increased. A urine protein-to-creatinine ratio (UPCR) does the same for total protein; a ratio above 3.5 g/g is nephrotic-range.

Anyone with diabetes should have a UACR at least yearly — albumin in the urine is the earliest sign of diabetic kidney disease and the point at which treatment changes the outcome. The same applies to high blood pressure, established kidney disease, a family history of kidney disease, heart failure, lupus and other autoimmune conditions, and long-term use of NSAIDs or lithium. Pregnancy brings its own rule: new protein after 20 weeks with a raised blood pressure is preeclampsia until proven otherwise.

Outside those groups, protein usually turns up on a routine urinalysis — for a physical, a sports clearance, a pre-employment or insurance exam, or a urine infection check — and the first question is simply whether it is still there on a properly collected repeat. Foamy or frothy urine, new ankle or eyelid swelling, or unexplained weight gain from fluid are reasons to test rather than wait for a routine check.

A complete urinalysis — dipstick plus microscopy — can be ordered online through TestWell and collected as a walk-in urine sample at a Labcorp patient service center; the urinalysis with reflex to culture is also offered at Quest. For the confirmatory ratio, order the urine albumin-to-creatinine ratio, which reports albumin, creatinine and the ratio on the same sample.

Collect a clean-catch midstream sample: wash hands, clean the area, pass the first part into the toilet and catch the middle portion. A first-morning sample is the most informative because it excludes the harmless orthostatic protein that appears only after hours upright; it is also the sample to use for a repeat. Skip hard exercise for 48 hours, do not collect during a fever or a urinary infection, and if you menstruate, wait or tell the lab, since blood contaminates the protein pad. Drink normally — neither water-loading nor dehydration — because the dipstick reads concentration.

Negative. Trace is a gray zone: common in concentrated urine and after exertion, and not abnormal on its own unless it keeps appearing or the person has diabetes, hypertension or kidney disease, in which case the UACR decides. 1+ or more on two or more samples taken weeks apart is persistent proteinuria and is always investigated.

In numbers, the UACR is the standard: below 30 mg/g normal, 30–300 moderately increased, above 300 severely increased. Daily protein excretion under 150 mg (about 0.15 g/g on the UPCR) is normal; 150 mg to 3.5 g is overt proteinuria; above 3.5 g a day is nephrotic-range, usually with low blood albumin, swelling and a high cholesterol. The dipstick can give a false positive in very alkaline urine (pH above 8), after antiseptics such as chlorhexidine contaminate the sample, with visible blood or pus, and in very concentrated urine; and a false negative in dilute urine or when the protein is not albumin.

Transient proteinuria is the most common kind and the kidney is fine: strenuous exercise within the last day or two, fever and acute illness, dehydration, cold exposure, emotional stress, seizures, heart failure flares and urinary infections can all push albumin through for a short time. Orthostatic (postural) proteinuria — protein only after being upright, absent in a first-morning sample — is found in a few percent of adolescents and young adults and is benign.

Persistent proteinuria means the filter or the tubules are damaged. Diabetes and high blood pressure account for most of it in adults; glomerular diseases (IgA nephropathy, membranous nephropathy, focal segmental glomerulosclerosis, lupus nephritis, minimal change disease), inherited conditions such as Alport syndrome, amyloidosis, preeclampsia in pregnancy, and drug injury (NSAIDs, gold, penicillamine, some cancer immunotherapies) make up the rest. Tubular proteinuria — small proteins the tubules fail to reabsorb — follows interstitial nephritis, heavy-metal exposure and some genetic disorders. Overflow proteinuria, where the blood simply carries too much of a small protein, is the myeloma pattern.

The amount tracks the cause. Trace to 1+ with a normal UACR is usually transient or orthostatic; a UACR of 30–300 mg/g is the early diabetic or hypertensive pattern; 3+ to 4+ with a UPCR above 3.5 g/g, swelling, a low albumin and a high cholesterol is nephrotic syndrome. Protein together with blood, red-cell casts and rising blood pressure is a nephritic picture and needs prompt nephrology input.

Repeat the dipstick on a first-morning clean-catch sample two or more weeks later, outside illness and exercise; if it is negative, that was transient or orthostatic proteinuria and no more is needed unless you have diabetes or hypertension. If it is still positive, quantify it with a UACR (or UPCR), and check serum creatinine with eGFR, a complete urinalysis with microscopy for blood, casts and cells, blood pressure, fasting glucose or hemoglobin A1c, and a lipid panel and albumin when the protein is heavy. A kidney ultrasound and a nephrology referral follow when the UACR exceeds 300 mg/g, the eGFR is below 60 or falling, there is blood with the protein, or the cause is not obvious. Protein-lowering treatment — ACE inhibitors or ARBs, SGLT2 inhibitors, blood-pressure and glucose control — starts at the moderately increased stage, which is why the early finding is the valuable one.