Microalbuminuria
Microalbuminuria is a term to describe a moderate increase in the level of urine albumin. It occurs when the kidney leaks small amounts of albumin into the urine, in other words, when an abnormally high permeability for albumin in the glomerulus of the kidney occurs. Normally, the kidneys filter albumin, so if albumin is found in the urine, then it is a marker of kidney disease. The term microalbuminuria is now discouraged by Kidney Disease Improving Global Outcomes and has been replaced by moderately increased albuminuria.
Causes
Higher dietary intake of animal protein, animal fat, and cholesterol may increase risk for microalbuminuria, and generally, diets higher in fruits, vegetables, and whole grains but lower in meat and sweets may be protective against kidney function decline.Associations
- Marker of vascular endothelial dysfunction
- An important prognostic marker for kidney disease
- * in diabetes mellitus
- * in hypertension
- * in post-streptococcal glomerulonephritis
- Increasing microalbuminuria during the first 48 hours after admission to an intensive care unit predicts elevated risk for acute respiratory failure, multiple organ failure, and overall mortality
- A risk factor for venous thromboembolism
Diagnosis
The level of albumin protein produced by microalbuminuria can be detected by special albumin-specific urine dipsticks, which have a lower detection threshold than standard urine dipsticks. A microalbumin urine test determines the presence of the albumin in urine. In a properly functioning body, albumin is not normally present in urine because it is retained in the bloodstream by the kidneys.Microalbuminuria can be diagnosed from a 24-hour urine collection or, more commonly, from elevated concentration in a spot sample. Both must be measured on at least two of three measurements over a two- to three-month period.
An albumin level above the upper limit values is called "macroalbuminuria", or sometimes just albuminuria. Sometimes, the upper limit value is given as one less to mark that the higher value is defined as macroalbuminuria.
To compensate for variations in urine concentration in spot-check samples, comparing the amount of albumin in the sample against its concentration of creatinine is helpful. This is termed the albumin/creatinine ratio and microalbuminuria is defined as ACR ≥3.5 mg/mmol or ≥2.5 mg/mmol, or with both substances measured by mass, as an ACR between 30 and 300 µg albumin/mg creatinine.
For the diagnosis of microalbuminuria, care must be taken when collecting sample for the urine ACR. An early-morning sample is preferred. The patient should refrain from heavy exercises 24 hours before the test. A repeat test should be done 3 to 6 months after the first positive test for microalbuminuria. Lastly, the test is inaccurate in a person with too much or too little muscle mass. This is due to the variation in creatinine level which is produced by the muscle.
| Individual | Lower limit | Upper limit | Unit | |
| 24h urine collection | 30 | 300 | mg/24h | |
| Short-time urine collection | 20 | 200 | µg/min | |
| Spot urine albumin sample | 30 | 300 | mg/L | |
| Spot urine albumin/creatinine ratio | Women | 3.5 | 25 or 35 | mg/mmol |
| Spot urine albumin/creatinine ratio | Women | 30 | 400 | μg/mg |
| Spot urine albumin/creatinine ratio | Men | 2.5 or 3.5 | 25 or 35 | mg/mmol |
| Spot urine albumin/creatinine ratio | Men | 30 | 300 | μg/mg |