What is the significance of 24-hour urine protein and monoclonal (M-protein) testing?

From the Guidelines

A 24-hour urine collection is essential for accurate quantification of monoclonal protein excretion in patients with suspected or confirmed plasma cell disorders like multiple myeloma, as it provides a reliable measurement of proteinuria and helps assess kidney involvement, disease severity, and response to therapy. This test involves collecting all urine over a complete 24-hour period in a container with preservative. For patients with monoclonal gammopathies, both serum and urine protein electrophoresis should be performed at diagnosis and during follow-up to monitor disease activity 1. The 24-hour collection is preferred over spot urine samples because it accounts for variations in protein excretion throughout the day and provides a more reliable measurement of Bence Jones proteins (free light chains). Proper collection technique is essential - the patient should discard the first morning void on day one, then collect all subsequent urine including the first void of the following morning. During collection, the container should be refrigerated.

Key Points

• The 24-hour urine collection cannot be replaced by a morning urine sample or random urine samples with analytes corrected relative to creatinine concentration 1.
• Immunofixation of an aliquot from a concentrated 24-hour urine collection is required to confirm the presence and type of heavy and light chain, even if there is no measurable protein and even if there is no peak on urine electrophoresis 1.
• Changes in the quantity of urinary monoclonal protein often correlate with disease progression or treatment effectiveness, making this an important tool in managing plasma cell disorders.
• The use of serum-free light-chain measurement is recommended for identifying and monitoring nonsecretory multiple myeloma (MM) 1.

From the Research

24-Hour Urine and Monoclonal Protein

• The presence of monoclonal protein in 24-hour urine is a key diagnostic feature of Bence-Jones myeloma, a type of multiple myeloma 2.
• A study found that the median excretion of Bence-Jones protein in 24-hour urine of multiple myeloma patients was 0.49 g/24h, with a range of 0.06-2.45 g/24h 2.
• The detection of monoclonal secretion in 24-hour urine is typically performed by immunofixation electrophoresis or urine protein electrophoresis 3, 4.
• Monoclonal gammopathy of undetermined significance (MGUS) is characterized by the presence of a monoclonal protein in serum or urine without evidence of multiple myeloma or other related disorders 5, 6.
• The concentration of Bence-Jones protein in urine can be an important factor in distinguishing between MGUS and multiple myeloma, with MGUS typically having a smaller amount of protein in urine (< 1 g/24 hr) 6.

Diagnostic Approaches

• Serum protein electrophoresis (SPE) and immunofixation electrophoresis (IFE) are commonly used tests for the screening and diagnosis of monoclonal gammopathies 3.
• Urine protein electrophoresis and urine IFE may also be used to identify Bence-Jones proteinuria 3, 4.
• The choice of diagnostic approach may vary depending on the laboratory and the specific clinical context 3.

Clinical Significance

• The presence of monoclonal protein in 24-hour urine can be a marker of underlying plasma cell dyscrasia, such as multiple myeloma or MGUS 2, 5.
• Patients with MGUS are at risk of progressing to multiple myeloma or other related disorders, and should be monitored regularly for signs of disease progression 5, 6.