Urine protein electrophoresis (UPEP) is analogous to the serum protein electrophoresis test and is used to detect monoclonal proteins (M-proteins) in the urine by an electrophoretic method. A 24-hour urine collection is necessary for determination of the total amount of protein excreted in the urine per day. The quantity of M-protein excreted is determined by measuring the size (percent) of the M-spike in the densitometer tracing and multiplying it by the total 24-hour urinary protein excretion. The amount of protein can be expressed as mg/dL or mg/L, but it is much more useful to report the M-protein in g/24 hours because of wide variability in the daily urinary volume. On UPEP, a urinary M-protein is seen as a dense localized band on agarose or a tall narrow peak on the densitometer tracing. Generally, the amount of urinary monoclonal protein correlates directly with the size of the plasma cell burden, as long as renal function is relatively normal. Other names: Bence-Jones protein test.
Normal range: negative or no monoclonal free light chains detected.
Use
All patients with a diagnosis of a plasma cell dyscrasia should have a baseline UPEP (and immunofixation) of an aliquot from a 24-hour urine collection. This test is essential for detection of the presence of potentially nephrotoxic concentrations of urinary light chains.
UPEP testing is subsequently required to detect progression and to monitor response to therapy in patients who have urinary monoclonal proteins at baseline.
UPEP (and immunofixation) has been used also as a standard screening test for patients in whom there is clinical suspicion for a monoclonal plasma cell proliferative disorder such as myeloma or primary amyloidosis. The serum free light chain assay can be used as an alternative method.
Quantitative determination of M-protein is useful in the response to chemotherapy or progression of disease.
Interpretation
Increased In
Various proteinuria states
Monoclonal plasma cell proliferative disorders such as myeloma or primary amyloidosis
Limitations
The 24-hour urine specimen requires no preservative and may be kept at room temperature during collection.
Immunofixation should be performed in these patients even if the routine urine analysis is negative for protein, 24-hour urine protein concentration is within normal limits, and electrophoresis of a concentrated urine specimen shows no globulin peak.
If the patient has nephrotic syndrome, the presence of a monoclonal light chain strongly suggests either primary amyloidosis (AL) or light chain deposition disease in almost all instances.