Complementarily of urine analysis and serum free light chain assay for assessing response treatment response:...

With the introduction of a new sensitive serum assay for monoclonal free light chains (FLC), there is a question as to whether or not traditional urine immunofixation electrophoresis (IFE) is still necessary. Therapy for B-cell disease has greatly improved in recent time so that noninvasive biomarkers that suggest complete remissions have become increasingly important. A Consensus Opinion stated that because of methodological imperfections, at concentrations of FLC <100 mg/l, urine IFE should supplement serum FLC ratio.

Examples are presented from a review of laboratory results and medical records from 3 patients on treatment after diagnosis of amyloidosis AL and multiple myeloma.

Monoclonal FLC was identified in urine by IFE while the κ/λ ratio from the serum FLC assay was within the reference range.

The results from these 3 cases suggest that as the FLC concentration drops, the serum FLC results may become more ambiguous. These results are consistent with guidelines cautioning about conclusions drawn from the serum FLC assay alone. Although more study is needed, the examples presented here illustrate that traditional urine IFE appear to adds important information regarding potential complete remissions and remains an important complementary assay to the serum FLC assay.