Isolated proteinuria (ICD-10-GM R80: Isolated proteinuria) refers to the excretion of proteins (albumin), especially albumins, as well as alpha-globulins and beta-globulins with the urine without abnormalities of the urine sediment and without restriction of the glomerular filtration rate (GFR). By definition, proteinuria is > 0.15 g/day (> 150 mg/day). Albuminuria:
- Microalbuminuria: 20-200 mg albumin/l urine or 30-300 mg albumin/24 h.
- Macroalbuminuria: > 300 mg albumin/24 h
The following forms of proteinuria are distinguished:
| Proteinuria forms | Marker proteins | Causes |
| Prerenal proteinuria | Kappa-lambda light chains, hemoglobin, myoglobin. | “Overflow proteinuria,” i.e., due to exceeding tubular reabsorption capacity because of oversupply of proteins. Plasmocytoma (multiple myeloma), intravascular hemolysis, rhabdomyolysis wake up (dissolution of striated muscle). |
| Renal (intrarenal) proteinuria. | selective-glomerular: albumin | Mild damage to the glomerular filter: minimal-change glomerulonephritis, early stage of diabetic and hypertensive nephropathy, early stage of autoimmune diseases with renal involvement, IgA nephritis |
| unselective-glomerular: albumin, IgG | Severe glomerular filter damage: acute glomerulonephritis, advanced diabetic and hypertensive nephropathy (nephrosclerosis), amyloidosis, systemic vasculitides, systemic lupus erythematosus (SLE), advanced EPH gestosis, orthostatic proteinuria/stress proteinuria | |
| tubular: alpha-1-microglobulin | Impaired tubular reabsorption: interstitial nephritis, pyelonephritis, analgesic nephropathy, tubulotoxic nephropathy | |
| mixed glomerular-tubular: albumin, alpha-1-microglobulin | Severe glomerular filter damage and impaired tubular reabsorption: advanced glomerulonephritis, late stage hypertensive and diabetic nephropathy | |
| Postrenal proteinuria | Alpha-2-macroglobulin; the alpha-2-macroglobulin/albumin quotient is particularly sensitive for this purpose | Tubular secretion: in the presence of inflammation or postrenal hemorrhage (urolithiasis, tumors) |
Several types of proteinuria may occur simultaneously in one patient. Nephrotic syndrome is a special type of proteinuria. It is a symptom complex that includes the following symptoms:
- Proteinuria > 3.0-3.5 g/day [“large” proteinuria].
- Hypoproteinemia – decreased protein content in the blood.
- Hypalbuminemic edema – formation of water retention that occurs due to the decreased presence of certain proteins (albumin) in the body (when serum albumin < 2.5 g/day)
- Hyperlipidemia – increased blood lipids.
Proteinuria can be a symptom of numerous diseases (see under “Differential diagnoses”) and is considered an independent progression factor (factor for the progression) of renal insufficiency (kidney weakness). Prevalence: In children and adolescents, proteinuria is present in about 10% of all urine tests. This is usually only transient/transient proteinuria or intermittent. However, in about 0.1% of children, proteinuria is persistent and detectable in more than three consecutive urine samples. Course and prognosis: Course and prognosis depend on the cause of the disease. In any case, proteinuria must be medically clarified. Proteinuria has a high prognostic significance for the overall morbidity (frequency of disease) and mortality (number of deaths in a certain period of time, related to the number of the population concerned)! Screening for proteinuria should be performed in people over 60 years of age, diabetics and hypertensives to detect renal and cardiovascular risk early.
