Role of Urine Tests in Multiple Myeloma Diagnosis and Monitoring
Urine testing is essential for diagnosing and monitoring multiple myeloma, with 24-hour urine collection for protein electrophoresis and immunofixation being a mandatory component of the standard diagnostic workup. 1
Diagnostic Role of Urine Testing
- A 24-hour urine collection for protein electrophoresis and immunofixation is required to detect and characterize Bence Jones proteins (monoclonal free light chains) that may be excreted in the urine of multiple myeloma patients 1
- Random urine samples are insufficient and cannot replace a 24-hour urine collection, even when corrected for creatinine concentration 1
- Urine testing is particularly important for identifying light chain multiple myeloma, where free light chains may be the predominant or only monoclonal protein present 2
- Urine protein electrophoresis should be performed on a concentrated sample from the 24-hour collection to improve detection sensitivity 1
Specific Components of Urine Testing
- Urine protein electrophoresis (UPEP) identifies the presence of a monoclonal protein as a homogeneous peak in the densitometer tracing 1
- Urine immunofixation electrophoresis (UIFE) confirms the presence and type of heavy and light chains, even if there is no measurable protein or visible peak on electrophoresis 1
- Quantification of the 24-hour urinary protein excretion helps determine the tumor burden and serves as a baseline for monitoring treatment response 1
Relationship with Serum Testing
- Urine testing should be performed alongside serum protein electrophoresis, immunofixation, and serum free light chain assays for comprehensive evaluation 1, 3
- While serum free light chain assays are highly sensitive, they cannot completely replace 24-hour urine studies for patients with measurable urinary M-protein 2
- In some cases, Bence Jones proteins may be detected in urine but not in serum, making urine testing crucial for diagnosis 4
Role in Monitoring Disease
- Serial measurements of urinary M-protein are used to assess treatment response and disease progression 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
Emerging Approaches
- Recent research suggests that serum free light chain measurements might help reduce the need for urine testing in some cases 5
- A proposed algorithm using serum free light chain ratio and the difference between involved and uninvolved free light chains could potentially eliminate the need for up to 42% of urine studies with 93.9% sensitivity 5
- However, this approach is still investigational and has not been incorporated into current guidelines 5
Practical Considerations
- The detection limit for Bence Jones proteins using high-resolution gel electrophoresis is approximately 20 mg/L 6
- Factors such as renal catabolism, reabsorption, and losses during concentration can affect urinary Bence Jones protein levels 4
- For patients with light chain multiple myeloma, monitoring both serum and urine free light chains may provide more comprehensive disease assessment 7
Pitfalls to Avoid
- Failing to collect a complete 24-hour urine sample can lead to false-negative results 1
- Inadequate concentration of urine samples may reduce sensitivity for detecting low levels of monoclonal proteins 1
- Relying solely on serum testing without urine studies may miss some cases of multiple myeloma, particularly light chain variants 4
- Immunofixation should be performed even if there is no measurable protein or visible peak on electrophoresis to avoid false negatives 1