Biomarker: Albumin, urine

Overview

Urine albumin is a test that measures the amount of albumin, a major blood protein, excreted in the urine and is a key indicator of kidney filtration function. Albumin is normally retained in the bloodstream by healthy glomeruli; detectable or increased albumin in urine (albuminuria) reflects kidney damage and is strongly associated with chronic kidney disease, cardiovascular disease, and increased mortality. Mildly elevated levels, often called microalbuminuria or moderately increased albuminuria, are an early marker of diabetic nephropathy and generalized vascular disease. Clinically, urine albumin measurement is useful for diagnosing kidney disease, stratifying risk, and monitoring progression and treatment response, especially in people with diabetes, hypertension, or other kidney risk factors.

Clinical Use Cases

Screening for early kidney damage in people with diabetes (type 1 and type 2) and hypertension.
Diagnosing and staging chronic kidney disease together with estimated glomerular filtration rate (eGFR).
Monitoring progression of diabetic nephropathy and other kidney diseases over time.
Guiding and monitoring response to therapies that reduce kidney and cardiovascular risk, such as ACE inhibitors or angiotensin receptor blockers in patients with albuminuria.
Assessing cardiovascular risk, as albuminuria is associated with higher rates of heart attack, stroke, and all-cause mortality.
Evaluating kidney involvement in metabolic syndrome and other conditions associated with vascular damage.
Population surveillance and epidemiologic studies of renal and cardiovascular disease risk, for example in NHANES data.

Specimen Types

Spot (random) urine sample, often early-morning urine.
24‑hour urine collection.

Measurement Methods

Quantitative urine albumin assays on automated analyzers (for example, immunoassays) used in clinical laboratories.
Measurement of urine albumin concentration in mg/L, followed by calculation of excretion rate or ratio to creatinine.
Urine albumin‑to‑creatinine ratio (uACR) in a spot urine sample, recommended as the preferred screening and monitoring method.
Semi‑quantitative dipstick protein tests for gross proteinuria (not sensitive enough for microalbuminuria but sometimes used in initial screening).

Test Preparation and Influencing Factors

Collection timing: early‑morning spot urine is commonly recommended to reduce variability and is preferred for albumin‑to‑creatinine ratio measurement.
Need for confirmation: abnormal albumin results are typically confirmed on two out of three samples over several months due to biological and analytical variability.
Recent vigorous exercise, acute illness, fever, urinary tract infection, or marked hyperglycemia can transiently increase urine albumin and may lead to false‑positive results.
Blood pressure and glycemic control influence albumin excretion; poor control is associated with higher urine albumin levels.
Certain medications, especially drugs affecting renal hemodynamics (for example, ACE inhibitors, ARBs), can lower albuminuria and are used therapeutically; medication changes can therefore affect serial measurements.
Hydration status and urine concentration affect albumin concentration; using uACR helps correct for urine dilution via creatinine.
Pregnancy and some systemic conditions (for example, severe heart failure) may alter renal protein handling and albumin excretion.