Comparison of Free Light Chain Assays: Freelite and N Latex in Diagnosis, Monitoring, and Predicting Survival in Light Chain Amyloidosis

OBJECTIVES

Measurement of serum free light chains (FLCs) is critical in diagnosis, prognosis, and monitoring treatment responses in light chain (AL) amyloidosis. We compare the Freelite assay (polyclonal antibodies to hidden light chain epitopes), which is the current gold standard, with a new assay: a mixture of monoclonal antibodies to light chain epitopes (N Latex).

METHODS

We collected 240 serum samples from 94 consecutive patients with newly diagnosed AL amyloidosis (at least three serial serum samples during the first 6 months) analyzed at the National Amyloidosis Centre, London, from January 2011 to April 2012. Concordance in detecting abnormal light chain components and hematologic response was assessed at 2, 4, and 6 months.

RESULTS

The κ and λ clonal light chain involvement was 21% and 79%, respectively, with an abnormal κ/λ ratio or detectable protein in 78.7%. Median κ, λ, and difference in involved and uninvolved FLCs by Freelite and N Latex assays were 17.3 vs 16 mg/L (R(2 ) = 0.91), 48.8 vs 52.6 mg/L (R(2) = 0.52), and 43.2 vs 39.1 mg/L, respectively. Discordant κ/λ ratios at presentation were as follows: 10 of 90 abnormal by Freelite/normal by N Latex and 11 of 90 abnormal by N Latex/normal by Freelite.

CONCLUSIONS

Both FLC assays show good correlation in detecting the abnormal light chain subtype with discordance in absolute values and thus are not interchangeable.

The role of immunological assessment in patients with acute kidney injury and possible myeloma

Acute kidney injury (AKI) in plasma cell multiple myeloma (MM) is a medical emergency requiring a rapid, accurate diagnosis because prompt commencement of therapy and supportive care are essential. Most cases of AKI in MM are caused by cast nephropathy secondary to high levels of nephrotoxic serum free light chains (FLCs). This article reviews the role and relevance of FLC as an immunological biomarker for AKI and MM. We discuss the utility of FLC measurement as a screening tool in the cast nephropathy clinical setting. We present its analytical pitfalls and evolving evidence for the integration of an FLC assay into clinical algorithms.

Outcome in Renal AL Amyloidosis After Chemotherapy

Purpose

Chemotherapy in AL (primary or light chain) amyloidosis is associated with improved survival, but its effect on renal outcome has not been examined systematically. The purpose of this study was to evaluate the effect of chemotherapy on clinical outcome among patients with renal AL amyloidosis.

Patients and Methods

We evaluated factors influencing survival among 923 patients with renal AL amyloidosis observed during a 21-year period, including 221 patients who became dialysis dependent. Factors associated with renal outcome were analyzed, including serum free light chain (FLC) response to chemotherapy using a simple subtraction formula applicable to all stages of chronic kidney disease. Patient survival and graft survival were analyzed in 21 renal transplantation recipients.

Results

Median survival from diagnosis for the whole cohort was 35.2 months. Magnitude of FLC response with chemotherapy was strongly and independently associated with overall survival (P < .001) and renal outcome. Evaluable patients achieving more than 90% FLC response had a significantly higher rate of renal responses and lower rate of renal progression compared with patients achieving a 50% to 90% response, whose renal outcomes were, in turn, better than patients achieving less than 50% FLC response (P < .001). Median survival from dialysis dependence was 39.0 months, and median survival from renal transplantation was 89.0 months.

Conclusion

Renal outcome and overall outcome in AL amyloidosis are strongly associated with FLC response to chemotherapy and are best among patients achieving more than 90% suppression of the amyloidogenic monoclonal component. Survival on dialysis was substantially superior to that previously reported, and renal transplantation should be considered in selected patients with AL amyloidosis with end-stage renal disease.