Proteinuria is a classic sign of kidney disease and its presence carries powerful prognostic information. Although proteinuria testing is enshrined in clinical practice guidelines, there is surprising variation among such guidelines as to the definition of clinically significant proteinuria. There is also poor agreement as to whether proteinuria should be defined in terms of albumin or total protein loss, with a different approach being used to stratify diabetic and non-diabetic nephropathy. Further, the role of reagent strip devices in the detection and assessment of proteinuria is unclear. This review explores these issues in relation to recent national and international guidelines on chronic kidney disease (CKD) and epidemiological evidence linking proteinuria and clinical outcome. The authors argue that use of urinary albumin measurement as the front-line test for proteinuria detection offers the best chance of improving the sensitivity, quality and consistency of approach to the early detection and management of CKD.

https://journals.sagepub.com/doi/pdf/10.1258/acb.2009.009007

How should proteinuria be detected and measured

Proteinuria: detection and role in native renal disease progression.

We adapted the pyrogallol red-molybdate method for total urinary protein to the Cobas Bio centrifugal analyzer. The method is simple, rapid, sensitive, and inexpensive. Addition of 25 mg of sodium dodecyl sulfate per liter to the reagent modifies protein reactivities so that the chromogenicity of human gamma globulins is the same as that of albumin. Results by this method and a comparison method that included gel filtration and a modified biuret reaction correlated well (r = 0.951).

An improved pyrogallol red-molybdate method for determining total urinary protein.

Gentamicin (GM) is an antibiotic widely used in treating severe gram-negative infections. However, its clinical use is limited by its nephrotoxicity. Several lines of evidence indicate that free radicals are important mediators of gentamicin nephrotoxicity. Therefore, the aim of this work was to investigate the possible protective effect of the flavonoid quercetin, an antioxidant, on gentamicin-induced nephrotoxicity. For this purpose, rats were divided into four groups. First group served as a control and injected with the normal saline, second group was injected with quercetin (50 mg/kg/d, per os) for 7 d, third group was injected with gentamicin (80 mg/kg/d, intraperitoneally) for 7 d and the fourth group of animals was injected with quercetin plus gentamicin simultaneously for 7 d. Total protein levels were estimated in 24-h urine samples to assess kidney dysfunction. The rats were sacrificed on the seventh day and kidneys were collected for histopathological studies. Blood urea nitrogen (BUN) and creatinine levels were measured in the blood. Moreover, glutathione (GSH), lipid peroxide (TBARS) levels, superoxide dismutase (SOD) and catalase (CAT) activities were determined in renal tissues. GM-treated rats showed early kidney dysfunction as urinary total protein, BUN and serum creatinine levels were significantly increased. The significant decrease in GSH levels, SOD, CAT activities and increase in TBARS levels, indicated that GM-induced nephrotoxicity was mediated through oxidative stress reactions. Histopathological examination of GM-treated rats revealed degenerative changes in glomeruli and tubules. On the other hand, simultaneous administration of quercetin plus gentamicin protected kidney tissues against nephrotoxic effects of gentamicin as evidenced from amelioration of histopathological changes and normalization of kidney biochemical parameters.

Protective Effect of Quercetin against Gentamicin-Induced Nephrotoxicity in Rats

Kidney Function Tests

We used human serum protein fractions to evaluate the sensitivity and bias of three turbidimetric methods for determining concentrations of proteins. Each fraction (Cohn Fractions II, III, IV, and V) was assigned a protein concentration value that was determined by the biuret method, which we calibrated with purified monomer of human serum albumin. All three turbidimetric methods (those involving sulfosalicylic acid/sodium sulfate, trichloroacetic acid, and alkaline benzethonium chloride) gave acceptable results for Fraction V with crystallized human serum albumin as the reference material, but there was bias by each of the three methods for the three globulin fractions. The method involving alkaline benzethonium chloride with measurement at 450 nm had the best sensitivity within the range of linearity and the most consistent bias among the three globulin fractions. These results define the dilemma for valid calibration of these methods for total serum protein in cerebrospinal fluid and urine.

R J Elin

Papers

Three turbidimetric methods for determining total protein compared