Microalbuminuria
Encyclopedia
Microalbuminuria occurs when the kidney leaks small amounts of albumin
into the urine, in other words, when there is an abnormally high permeability
for albumin in the renal glomerulus.
produced by microalbuminuria can be detected by special albumin-specific urine dipstick
s. 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 (between 30–300 mg/24 hours) or, more commonly, from elevated concentrations in a spot sample (30 to 300 mg/L). 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 (such as 300 being given as 299) to mark that the higher value (here 300) is defined as macroalbuminuria.
To compensate for variations in urine concentration in spot-check samples, it is helpful to compare the amount of albumin in the sample against its concentration of creatinine
. This is termed the albumin/creatinine ratio (ACR) and microalbuminuria is defined as ACR ≥3.5 mg/mmol (female) or ≥2.5 mg/mmol(male), 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.
Human serum albumin
Human serum albumin is the most abundant protein in human blood plasma. It is produced in the liver. Albumin constitutes about half of the blood serum protein...
into the urine, in other words, when there is an abnormally high permeability
Vascular permeability
Vascular permeability, often in the form of capillary permeability, characterizes the capacity of a blood vessel wall to allow for the flow of small molecules or even whole cells in and out of the vessel. Blood vessel walls are lined by a single layer of endothelial cells...
for albumin in the renal glomerulus.
Diagnosis
The level of albumin proteinProtein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
produced by microalbuminuria can be detected by special albumin-specific urine dipstick
Dipstick
A dipstick is one of several measurement devices.Some dipsticks are dipped into a liquid to perform a chemical test or to provide a measure of quantity of the liquid....
s. 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 (between 30–300 mg/24 hours) or, more commonly, from elevated concentrations in a spot sample (30 to 300 mg/L). 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
Albuminuria
Albuminuria is a pathological condition wherein albumin is present in the urine. It is a type of proteinuria.Measurement=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...
. Sometimes, the upper limit value is given as one less (such as 300 being given as 299) to mark that the higher value (here 300) is defined as macroalbuminuria.
To compensate for variations in urine concentration in spot-check samples, it is helpful to compare the amount of albumin in the sample against its concentration of creatinine
Creatinine
Creatinine is a break-down product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body...
. This is termed the albumin/creatinine ratio (ACR) and microalbuminuria is defined as ACR ≥3.5 mg/mmol (female) or ≥2.5 mg/mmol(male), 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 (milligram albumin per 24 hours) | |
| Short-time urine collection | 20 | 200 | µg/min (microgram Microgram In the metric system, a microgram is a unit of mass equal to one millionth of a gram , or 1/1000 of a milligram. It is one of the smallest units of mass commonly used... albumin per minute) |
|
| Spot urine albumin sample | 30 | 300 | mg/l (milligram albumin per litre Litre pic|200px|right|thumb|One litre is equivalent to this cubeEach side is 10 cm1 litre water = 1 kilogram water The litre is a metric system unit of volume equal to 1 cubic decimetre , to 1,000 cubic centimetres , and to 1/1,000 cubic metre... of urine) or µg/g (microgram albumin per gram of urine) |
|
| Spot urine albumin/creatinine ratio | Women | 3.5 | 25 or 35 | mg/mmol (milligram albumin per millimole creatinine) |
| 30 | 300 | μg/mg (microgram albumin per milligram creatinine) | ||
| Men | 2.5 or 3.5 | 25 or 35 | mg/mmol | |
| 30 | 300 | μg/mg |
Significance
- an indicator of subclinical cardiovascular disease
- marker of vascular endothelial dysfunctionEndothelial dysfunctionEndothelial dysfunction is a systemic pathological state of the endothelium and can be broadly defined as an imbalance between vasodilating and vasoconstricting substances produced by the endothelium...
- an important prognostic marker for kidney disease
- in diabetes mellitusDiabetes mellitusDiabetes mellitus, often simply referred to as diabetes, is a group of metabolic diseases in which a person has high blood sugar, either because the body does not produce enough insulin, or because cells do not respond to the insulin that is produced...
- in hypertensionHypertensionHypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...
- in diabetes mellitus
- increasing microalbuminuria during the first 48 hours after admission to an intensive care unitIntensive Care Unitthumb|220px|ICU roomAn intensive-care unit , critical-care unit , intensive-therapy unit/intensive-treatment unit is a specialized department in a hospital that provides intensive-care medicine...
predicts elevated risk for acute respiratory failureRespiratory failureThe term respiratory failure, in medicine, is used to describe inadequate gas exchange by the respiratory system, with the result that arterial oxygen and/or carbon dioxide levels cannot be maintained within their normal ranges. A drop in blood oxygenation is known as hypoxemia; a rise in arterial...
, multiple organ failure, and overall mortality - a risk factor for venous thromboembolism