When is urine electrophoresis recommended and what are the implications of its results?

Urine Electrophoresis in Multiple Myeloma

Urine electrophoresis is an essential diagnostic test for suspected multiple myeloma, required to detect Bence Jones proteins (monoclonal free light chains) that may be excreted in urine, and should be performed using a 24-hour urine collection with both electrophoresis and immunofixation. 1, 2

Indications for Urine Electrophoresis

• Recommended as part of the standard initial workup for all patients with suspected multiple myeloma or related plasma cell disorders 1
• Required for comprehensive evaluation even when serum tests are performed, as some patients may have significant urinary monoclonal protein without detectable serum abnormalities 2
• Essential for diagnosing light chain multiple myeloma, where serum protein electrophoresis may be normal but urine shows monoclonal light chains 2, 3
• Necessary for monitoring disease response to treatment in patients with measurable urinary M-proteins 2

Proper Collection and Processing Methods

• A complete 24-hour urine collection is mandatory and cannot be replaced by random urine samples, even when corrected for creatinine concentration 1, 2
• An aliquot from the 24-hour specimen must be adequately concentrated before electrophoresis to improve detection sensitivity 1, 2
• Both urine protein electrophoresis (UPEP) and urine immunofixation electrophoresis (UIFE) should be performed 1
• Immunofixation should be performed even if there is no measurable protein or visible peak on electrophoresis to avoid false negatives 1, 2

Interpretation of Results

• A monoclonal protein appears as a homogeneous peak in the densitometer tracing on UPEP 1
• The concentration of monoclonal protein can be calculated based on the size of the peak and total protein in the 24-hour specimen 1
• UIFE confirms the presence and type of heavy and light chains 1, 2
• Approximately 20% of newly diagnosed multiple myeloma patients have secretory urinary proteins 1
• About 3% of patients have neither serum nor urine proteins (nonsecretory myeloma) 1

Clinical Implications of Results

• Presence of monoclonal light chains in urine (Bence Jones protein) supports the diagnosis of multiple myeloma, amyloidosis, or other plasma cell disorders 4
• Quantification of urinary M-protein serves as a baseline for monitoring treatment response 2
• Complete response criteria include negative immunofixation of both serum and urine 2
• Partial response is defined as ≥50% reduction of serum M-protein and ≥90% reduction in 24-hour urinary light chain excretion or to <200 mg/24h 2

Relationship with Other Tests

• Urine testing should be performed alongside serum protein electrophoresis, immunofixation, and serum free light chain assays for comprehensive evaluation 2
• While serum free light chain assays have shown greater sensitivity than urine electrophoresis in some studies 3, 5, guidelines still recommend performing both tests 1
• The combination of serum protein electrophoresis and serum free light chain analysis has shown 100% sensitivity for detecting plasma cell disorders in some studies 5

Common Pitfalls to Avoid

• Incomplete 24-hour urine collection leading to false-negative results 2
• Inadequate concentration of urine samples reducing sensitivity 2, 6
• Relying solely on the Bence Jones heat test, which can yield both false-positive and false-negative results 4
• Failing to perform immunofixation when electrophoresis shows no visible peak 1, 2
• Using random urine samples instead of a complete 24-hour collection 1, 2