Proteinuria—take a closer look!

Abstract

Proteinuria is a hallmark of kidney disease. Therefore, measurement of urine protein content plays a central role in any diagnostic work-up for kidney disease. In many cases, proteinuria analysis is restricted to the measurement of total protein content knowing that very high levels of proteinuria (nephrotic proteinuria) are characteristic of glomerular disease. Still, proteinuria can also be a manifestation of impaired tubular protein reabsorption or even be physiological. This review will discuss the physiology of renal protein handling and give guidance on a more sophisticated analysis of proteinuria differentiating albumin, low-molecular weight proteins and immunoglobulins. These non-invasive tests are available in most routine clinical laboratories and may guide the clinician in the diagnostic process before ordering far more expensive (molecular genetic testing) and/or invasive (kidney biopsy) diagnostics.

A riddle wrapped in an enigma: acute kidney injury in a girl with Crohn’s disease: Answers

“…Blood tests may show anemia, eosinophilia, elevated C-reactive protein, and erythrocyte sedimentation rate. Urinalysis is characterized by sterile pyuria with WBC casts, hematuria, and non-nephrotic range proteinuria of tubular origin [ 7 , 8 ]. Granular casts and eosinophiluria may also be found.…”

Comparison of Two Different Semiquantitative Urinary Dipstick Tests with Albumin-to-Creatinine Ratio for Screening and Classification of Albuminuria According to KDIGO. A Diagnostic Test Study

“…The semiquantitative total urine protein detection with the Combour9-Test ® is based on the ability of the protein to change the dye color of an acid–base indicator, forming the anion of 3′,3″,5′,5″-tetrachlorphenol-3,4,5,6-tetrabromsulfophthalein in presence of protein in the urine, resulting in a gradational change of the indicator dye [ 24 ]. Although the Combur9-Test ® aims for total protein in the urine, the sensitivity to albumin is higher than to other proteins found in the urine; this is explained by the increased affinity of albumin to protons [ 24 , 25 , 26 ]. The rational in our study to consider a Combur9-Test ® value of ≥15–30 mg/dL (1+) as positive is based on the statement in the KDIGO 2012 guidelines that a reagent strip with (1+) protein positivity can substitute a quantitative albuminuria measurement where it not available [ 13 ].…”

Oxidized Albumin as a Mediator of Kidney Disease

“…Circulating albumin is filtered in small amounts at renal level (<4 mg/m 2 /h). However, three physiological situations lead to albumin presence in urine: postural, febrile, and exercise [ 14 , 16 ]. In all these circumstances, albuminuria is transiently elevated but absent when urine collection is performed first thing in the morning, after a feverish period, or post-recovery from strenuous exercise, respectively.…”

“…In all these circumstances, albuminuria is transiently elevated but absent when urine collection is performed first thing in the morning, after a feverish period, or post-recovery from strenuous exercise, respectively. Considering the above, in normal conditions, the glomerular barrier prevents the majority of albumin filtration due to its size and negative charge [ 16 ].…”