Evaluation of Proteinuria in Plasma Cell Disorders: Shortcomings of Measurements Based on 24-Hour Collections and Alternative Approaches.

Background: Clonal plasma cell disorders, such as multiple myeloma (MM), often cause excretion of monoclonal free light chains (MFLC) into urine that serve as diagnostic markers and can cause renal injury.

Content: Measures of urinary protein excretion (PEx) and MFLC excretion are parameters for diagnosing and managing plasma cell disorders, although the roles are evolving as new diagnostic tools are applied. Current guidelines dictate measuring PEx and MFLC excretion using 24-hour urine specimens, which have multiple shortcomings that compromise the quality of testing, delay results, and are burdensome for patients. These problems raise consideration of alternatives to the 24-hour PEx (24-hPEx). Such changes in practice have occurred for evaluating proteinuria in many other disorders. Calculating an estimated 24-hPEx based on urine protein/creatinine ratios on spot specimens is one option that overcomes many shortcomings of the measured 24-hPEx. Random urine specimens also probably are preferable for qualitative testing (absence or presence of MFLC) for diagnostic applications and MM response monitoring.

Summary: Measurement of PEx and MFLC excretion using 24-hour collections is unreliable, inconvenient, and delays evaluation of plasma cell disorders. Estimated 24-hPEx based on protein assays of spot urine specimens overcomes many of these problems and should be evaluated by further studies. Changing routine practice requires guideline and protocol modification and action by laboratories to increase availability of testing and calculated values. Issues described here also have relevance to evaluating proteinuria in other disorders.