Albumin

Norm     
35–50g/l

Serum
Red cap

Albumin makes up about 60% of the total blood protein content. It is synthesized in the liver (approximately 15g per day). Albumin forms the basis of oncotic plasma pressure and therefore maintains the volume of circulating blood. Albumin is the main transport protein in the body. This protein transports calcium, manganese, zinc, hormones, and medications. Sometimes, changes in the concentrations of calcium and other substances may be related to significant fluctuations in albumin concentration. Therefore, when determining the concentration of calcium or other substances, it may be necessary to make an “adjustment” with respect to albumin. Usually, such adjustment is not necessary if the albumin concentration has changed only slightly.   

A strip urine analyzer test cannot detect low albumin concentrations in urine. This circumstance led to the introduction of the incorrect term “microalbuminuria” into clinical practice. Microalbuminuria is considered when there is a constant (detected at least three times a week) excretion of albumin in urine at 20-200 mg/l (0.02-0.2g/l). The detection of microalbuminuria is necessary in cases of diabetes or hypertension. In the stage of microalbuminuria, changes in the glomerular basement membrane are still reversible and can be corrected. Using a strip urine analyzer, “macroalbuminuria” can be determined when there is around 250 mg/l (0.25g/l) of albumin and more. This is already a late stage of albuminuria where therapeutic intervention is less effective, kidney function impairments progress rapidly. When the basement membrane irreversibly changes, not only low molecular weight proteins (albumins) but also all other serum proteins start to differ in urine (this can be detected, for example, by measuring the amount of immunoglobulin G in urine). This proteinuria, when all serum proteins differ, is called “nonselective” proteinuria. Besides diabetes and hypertension, microalbuminuria is an independent prognostic factor for coronary heart disease (unfavorable prognosis). Albumin levels higher than 200 mg/l are characteristic of glomerular albuminuria.

Source | Handbook of Basic Laboratory Tests | Doctor of Medical Sciences Gintaras Zaleskis