A double antibody radioimmunoassay for human alpha 1-microglobulin

Rapid screening of low molecular mass proteinuria: evaluation of the first immunochemical test strip for the detection of alpha 1-microglobulin in urine

A new semiquantitative immunochemical test strip for urinary alpha 1-microglobulin, a marker protein for tubular proteinuria, was assessed. This test strip has four colour zones, reflecting alpha 1-microglobulin concentrations of ca. 10, 25, 50, and 80 mg/l. alpha 1-Microglobulin concentrations were measured by means of the test strip and an immunonephelometric method in 330 samples collected as the second voided morning urine. The reading time of the test strip must be strictly observed. Reading one minute earlier or later than the 5 min stated in the instructions led to misclassification of over 70% of the results. Correlation between both methods was highly significant, with a Spearman rank correlation coefficient of rs = 0.84 (P < 0.001). There was a partial overlap of the test strip results in different concentration ranges. An elevation of alpha 1-microglobulin was defined as > 25 mg/l, calculated as the upper limit of the central 95% interval of alpha 1-microglobulin concentration in urine samples measured in a previous study of 304 healthy adults. Using this definition of alpha 1-microglobulin elevation, a sensitivity of 97.5%, specificity of 73.6%, a false-positive rate of 16.6%, and a false-negative rate of 0.9% of the test strip results were obtained. A fraction of 82.4% of the 330 samples investigated was correctly classified as having increased alpha 1-microglobulin concentration or not. Methodical improvements of the test strip are necessary to reduce overlapping results, in order to make the test suitable for screening purposes.

Human alpha 1-microglobulin: its measurement and clinical significance

alpha 1-Microglobulin (alpha 1-M), also called protein HC, is a low-molecular-weight (LMW) glycoprotein (about 30 kDa) with unique physicochemical properties. Using purified urinary alpha 1-M a standard and specific antibody against alpha 1-M, an assay system for alpha 1-M was developed, and the clinical significance of this protein was investigated by measuring total levels of alpha 1-M under physiological and pathological conditions. alpha 1-M is distributed in various body fluids: in serum, it consists mainly of free LMW alpha 1-M and monomeric IgA-alpha 1-M complex. The total alpha 1-M level in serum and urine usually reflects LMW alpha 1-M variation sensitively, and its determination is quite useful as an indicator of renal glomerulotubular dysfunction and hepatic dysfunction. Serum levels can vary, depending on IgA-alpha 1-M complex level, in parallel with the IgA concentration. The heterogeneity of alpha 1-M purified from different sources of urine by different procedures and underestimation of IgA-alpha 1-M complex by solid-phase antibody assays can be important causes for the discrepancy of serum levels between assays.

Measurement of protein HC (alpha 1 microglobulin) and protein HC-IgA complex in different body fluids

Protein HC and protein HC-IgA complex were measured in 18 different types of fluid sample from healthy subjects and patients with different illnesses to determine if the concentrations of protein HC and protein HC-IgA complexes could be used to monitor certain diseases, when measured separately. The normal values for HC ranged from between 0.30 mg/l in saliva and 11.7 mg/l in blood plasma. HC-IgA complex has a greater range, from undetectable concentrations (urine, colostrum, and cervical mucus) up to 59.2 mg/l in blood plasma. Undetectable concentrations of HC-IgA complex were also shown in serum from patients with IgA immune deficiency and in cerebrospinal fluid from patients with multiple sclerosis. Increased concentrations of HC were noted in bronchoalveolar fluid from a patient with pulmonary alveolar proteinosis, serum from patients with Behcet's syndrome, and in synovial fluid from patients with gout, chondrocalcinosis, and rheumatoid arthritis. On the other hand, the concentrations of HC-IgA complex were raised only in those patients with pulmonary alveolar proteinosis or rheumatoid arthritis.