Proteinuria

Proteinuria means there is more protein in the urine than normal. Healthy kidneys keep most protein in the blood, so lasting proteinuria is often an early sign of kidney damage. Common causes include diabetes and high blood pressure. Others include glomerulonephritis, lupus, preeclampsia in pregnancy, and some medicines. Short-lived proteinuria can happen with fever, hard exercise, dehydration or standing for long periods (orthostatic proteinuria, mainly in young people). Proteinuria usually causes no symptoms. Large amounts can cause foamy urine and swelling around the eyes, ankles or legs.

Lab tests linked to proteinuria:

• Protein, total, random urine: measures protein in a single urine sample.
• Protein/creatinine ratio: compares urine protein with creatinine to estimate how much protein is lost in a day.
• Doctors often use the urine albumin-to-creatinine ratio (ACR) for people with diabetes or high blood pressure. They also check kidney function (creatinine and eGFR), blood pressure, glucose or HbA1c, and a urinalysis with microscopy. A kidney ultrasound or biopsy may follow.

How results are read:

• A urine protein/creatinine ratio above about 0.15 to 0.2 g/g (150 to 200 mg/g) is usually considered raised. Values above about 3.5 g/g suggest nephrotic-range protein loss.
• A single raised result is repeated, because fever, exercise and infection can raise it briefly. Lasting proteinuria on 2 of 3 tests over 3 months is significant.
• Proteinuria together with blood in the urine or a falling eGFR points to a kidney disease that needs specialist assessment.
• Orthostatic proteinuria is checked by comparing a first-morning urine sample with a daytime sample.

When to see a doctor:

• See a doctor to repeat a raised urine protein result, especially if you have diabetes, high blood pressure or a family history of kidney disease.
• See a doctor promptly about new swelling of the face, ankles or legs, or foamy urine.
• During pregnancy or in the weeks after birth, contact your maternity team immediately for a severe or persistent headache or vision changes, whether or not protein has been found in the urine. New protein in the urine with high blood pressure needs prompt maternity assessment.

Clinical takeaway: proteinuria is measured with a urine protein/creatinine or albumin/creatinine ratio, and lasting protein loss on repeat testing is a sign of kidney damage that needs a cause found.