Microalbuminuria

Microalbuminuria (Urine albumin) 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.

Diagnosis

The level of albumin protein produced by microalbuminuria can be detected by special albumin-specific 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 (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.^[1]

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.^[2]

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)^[3] and microalbuminuria is defined as ACR ≥3.5 mg/mmol (female) or ≥2.5 mg/mmol (male),^[4] or, with both substances measured by mass, as an ACR between 30 and 300 µg albumin/mg creatinine.^[5] 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.^[6]

Significance

• an indicator of subclinical cardiovascular disease
• 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 ^[9]

See also

• Albuminuria

References

• Abid O, Sun Q, Sugimoto K, Mercan D, Vincent JL (2001). "Predictive value of microalbuminuria in medical ICU patients: results of a pilot study". Chest 120 (6): 1984–8. doi:10.1378/chest.120.6.1984. PMID 11742932. 
• Andersen S, Blouch K, Bialek J, Deckert M, Parving HH, Myers BD (2000). "Glomerular permselectivity in early stages of overt diabetic nephropathy". Kidney Int. 58 (5): 2129–37. doi:10.1111/j.1523-1755.2000.00386.x. PMID 11044234. 
• Heart Outcomes Prevention Evaluation Study Investigators (2000). "Effects of ramipril on cardiovascular and microvascular outcomes in people with diabetes mellitus: results of the HOPE study and MICRO-HOPE substudy". Lancet 355 (9200): 253–9. doi:10.1016/S0140-6736(99)12323-7. PMID 10675071. 
• Lemley KV, Abdullah I, Myers BD et al. (2000). "Evolution of incipient nephropathy in type 2 diabetes mellitus". Kidney Int. 58 (3): 1228–37. doi:10.1046/j.1523-1755.2000.00223.x. PMID 10972685. 
• Lièvre M, Marre M, Chatellier G et al. (2000). "The non-insulin-dependent diabetes, hypertension, microalbuminuria or proteinuria, cardiovascular events, and ramipril (DIABHYCAR) study: design, organization, and patient recruitment. DIABHYCAR Study Group". Controlled Clinical Trials 21 (4): 383–96. doi:10.1016/S0197-2456(00)00060-X. PMID 10913814. 
• Parving HH, Lehnert H, Bröchner-Mortensen J, Gomis R, Andersen S, Arner P (2001). "The effect of irbesartan on the development of diabetic nephropathy in patients with type 2 diabetes". N. Engl. J. Med. 345 (12): 870–8. doi:10.1056/NEJMoa011489. PMID 11565519. 

Footnotes

External links

• Microalbumin and Urine Albumin/Creatinine Ratio – Lab Tests Online
• Online Microalbumin Urine Calculator
• first-ever large-scale clinical trial to evaluate whether an ARB can prevent the initial development of Microalbuminuria