# Albuminuria

Albuminuria is a pathological condition of elevated albumin protein in the urine (often measured as urine albumin-to-creatinine ratio of >30 milligrams of albumin per 1 gram of creatinine per day). It is a type of proteinuria, and is the most common protein detected on urinalysis that, when elevated, is associated with kidney and cardiovascular disease (CVD). Albumin is an abundant plasma protein (present in blood tissue) which is normally prevented from being lost into the urine by the sieve-like glomeruli of the nephrons. In healthy people, only trace amounts of it are present in urine, but when the filtration system of the kidney is damaged, larger amounts of albumin escape into the urine, which can be quantified and used to determine the extent of kidney injury/kidney disease.

## Signs and symptoms

Albuminuria is often asymptomatic in low quantities but foamy urine may be present. As significant albumin is lost to the urine, swelling of the ankles, hands, belly or face may occur (see edema and nephrotic syndrome). This is because a major role of albumin in the blood is to act as an osmotic agent, keeping water from leaving blood vessels and leaking into the surrounding body tissues.

## Causes

Albuminuria is not a disease itself but a marker of kidney injury, particularly to the filtration mechanism (glomerulus), and can be caused by a number of pathological states, including:
* Diabetic nephropathy
* Hypertension
* Various autoimmune disorders
** Lupus nephritis
** IgA nephropathy
** ANCA-associated vasculitis
** Anti-GBM disease (Goodpasture's syndrome)
** Membranous nephropathy
** Antiphospholipid syndrome
** Alport syndrome
** Sjogren syndrome
* Dehydration / low blood volume
* Cardiovascular disease
* Nephrotoxic medications
In all cases, the result is a loss of the kidney's ability to retain albumin from the urine.
The kidneys normally do not filter large molecules into the urine, so albuminuria can be an indicator of damage to the kidneys or excessive salt intake. It can also occur in patients with long-standing diabetes, especially type 1 diabetes. Recent international guidelines (KDIGO 2024) reclassified chronic kidney disease (CKD) based on cause, glomerular filtration rate category, and albuminuria category (A1, A2, A3).
Causes of albuminuria can be discriminated between by the amount of protein excreted.
* Microalbuminuria (between 30 and 300 mg/24h, mg/L of urine or μg/mg of creatinine) can be a forerunner of diabetic nephropathy. The term albuminuria is now preferred in Nephrology since there is not a "small albumin" (microalbuminuria) or a "big albumin" (macroalbuminuria). A1 represents normal to mildly increased urinary albumin/creatinine ratio (<30 mg/g or < 3 mg/mmol); A2 represents moderately increased urinary albumin/creatinine ratio (30–300 mg/g or 3–30 mg/mmol, previously known as microalbuminuria); and A3 reflects severely increased urinary albumin/creatinine ratio >300 mg/g or > 30 mg/mmol).

## Diagnosis

The amount of protein being lost in the urine can be quantified by collecting the urine for 24 hours, measuring a sample of the pooled urine, and extrapolating to the volume collected.
Alternatively, a urine dipstick test for proteinuria can give a rough estimate of albuminuria. This is because albumin is by far the dominant plasma protein, and bromophenol blue, the reagent used in the dipstick, is specific to albumin.

## Treatment

Though there is some evidence that dietary interventions (to lower red meat intake) can be helpful in lowering albuminuria levels, there is currently no evidence that low protein interventions correlate to improvement in kidney function. Among other measures, blood pressure control, especially with the use of inhibitors of the renin-angiotensin-system, is the most commonly used therapy to control albuminuria.