Classification of renal proteinuria: a simple algorithm.
Total protein, albumin, alpha1-microglobulin, and immunoglobulin G (IgG) were analyzed in 1,622 urine samples without Bence-Jones proteinuria or gross hematuria. There was correlation with the histological picture obtained on renal biopsy in 61 patients. We established 24-h reference intervals for alpha1-microglobulin and IgG on 659 urine samples with total protein and albumin excretion rates below 100 mg/24 h and 30 mg/24 h, respectively, and creatinine clearance above 80 ml/min. The central 95% reference interval was found to be between 4 and 17 mg/24 h for alpha1-microglobulin and between 3 and 8.5 mg/24 h for IgG. In 80 urine samples with albumin excretion rate above 30 mg/24 h and alpha1-microglobulin and IgG within their reference intervals, we analyzed the 95% central interval of the distribution of the IgG/albumin ratios, and it was found to be within 0.01 and 0.20 (0.90 confidence interval: 0.17-0.24). Proteinuria was considered to be of the selective glomerular type if the albumin excretion rate was abnormal and the IgG/albumin ratio was under 0.20, even when the IgG excretion was within a pathological range. For the classification of proteinuria as predominantly tubular, we estimated the alpha1-microglobulin/albumin ratio in 173 urine samples with normal excretion rates of albumin and IgG and pathological excretion of alpha1-microglobulin. The discriminating value of 0.91 (0.90 confidence interval: 0.78-1.08) was accepted in order to define proteinuria of a tubular origin in the presence of a pathological albumin excretion rate. The association between albumin and IgG excretion rates and tubular reabsorption of the alpha1-microglobulin normally filtered by the glomerulus was studied in 33 urine samples from patients with no histologically significant tubulo-interstitial or vascular disease and a serum creatinine concentration below 141 pmol/l. The optimal curve-fitting function between albumin plus IgG and alpha1-microglobulin excretion rates was of the quadratic type (r = 0.927). Mixed proteinuria was considered when both, albumin and alpha1-microglobulin excretion rates were pathological and could not be included in the previously described groups.
Bergón
Enrique
E
Department of Clinical Pathology, Hospital Universitario de Getafe, Madrid, Spain. ebergon@pobladores.com
Granados
Rosario
R
Fernández-Segoviano
Pilar
P
Miravalles
Elena
E
Bergón
Marta
M
D000465:Algorithms; D001707:Biopsy, Needle; D002940:Circadian Rhythm; D019411:Clinical Laboratory Techniques; D006801:Humans; D007074:Immunoglobulin G / Q000652:urine*; D007668:Kidney / Q000473:pathology; D007678:Kidney Glomerulus / Q000503:physiopathology; D007684:Kidney Tubules / Q000503:physiopathology; D008562:Membrane Glycoproteins / Q000652:urine*; D011507:Proteinuria / Q000145:classification* / Q000503:physiopathology / Q000652:urine*; D012016:Reference Values; D015203:Reproducibility of Results; D013223:Statistics as Topic / Q000379:methods; D014360:Trypsin Inhibitor, Kunitz Soybean
D007074:Immunoglobulin G; D008562:Membrane Glycoproteins; C109148:SPINT2 protein, human; D014360:Trypsin Inhibitor, Kunitz Soybean