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Evaluate myeloma, macroglobulinemia of Waldenström, lymphoma, amyloidosis; differentiate between normal renal function, glomerular proteinuria, and tubular proteinuria. Increased glomerular permeability leads to higher concentrations of large proteins in the glomerular filtrate. Diminished tubular reabsorptive capacity results in a marked increase in urinary excretion of low molecular weight problems.
May not detect pathologic light chains due to insufficient sensitivity. Should be followed with immunoelectrophoretic or immunofixation study performed on concentrated urine. Optimal specimen when looking for a free monoclonal light chain (Bence Jones protein) is a 24-hour collection.
A serum protein electrophoresis should be reviewed concurrently if one has not been recently studied. In nonselective glomerular proteinuria, the urine electrophoretic pattern is often a nonspecific one which may be called “mirror image” to that of the serum. Contamination of the urine with blood can give a similar pattern. With selective glomerular permeability, albumin, α1-proteins, and transferrin are the predominant proteins identified on the urine protein electrophoresis, with a relative absence of heavier molecular weight proteins (ie, α2-macroglobulin and immunoglobulins). With tubular proteinuria, low molecular weight proteins (α2- and β2-microglobulins) are predominant, with trace amounts of albumin. So called “overflow proteinuria” occurs when low molecular weight proteins are filtered through the glomerulus in increased amounts.
