Palladini et al.  compared response to treatment as assessed by Freelite and the Siemens N Latex FLC assays. Although the results produced by both assays were prognostic, percentage reductions in FLC concentration were quite different, leading the authors to conclude that amended response criteria would be needed for the N Latex FLC assays (Chapter 8).
28.7.1. sFLC response predicting cardiac outcomes
Organ responses are typically slow to appear in patients with AL amyloidosis and are usually dependent on an adequate haematological response. The presence of cardiac amyloidosis is the major prognostic determinant in AL amyloidosis. Although cardiac involvement is present in only approximately half of patients at diagnosis (Section 28.1), virtually all AL amyloidosis patients will die from cardiac-related sequelae . Measurement of cardiac biomarkers, namely troponin T and B-type natriuretic peptide (NT-proBNP) are useful in defining prognosis at diagnosis (Section 28.4), and should be monitored to assess response to therapy, in parallel with the assessment of haematological response .
The important link between improving cardiac function in AL amyloidosis and falling sFLC concentrations was first observed by Palladini and colleagues . Fifty-one AL amyloidosis patients with symptomatic myocardial involvement were given chemotherapy and monitored with sFLCs and NT-proBNP. During treatment, 22 patients had a reduction of sFLCs by more than 50%, including nine patients who had disappearance of monoclonal immunoglobulins as assessed by IFE; a corresponding reduction of NT-proBNP levels was also observed (p<0.001). Survival was superior in responders than in non-responders (p<0.001). This finding was supported by a subsequent study by Kastritis et al. , which confirmed by multivariate analysis that a cardiac response was associated with a haematological response (46% vs. 0% in non-haematological responders; p<0.001).
Further studies have demonstrated a direct cardiotoxic effect of amyloidogenic FLCs , and support the clinical observation that a reduction in circulating monoclonal FLCs translates into a rapid improvement in cardiac function. Therefore, it is important to reduce the concentrations of cardiotoxic FLCs promptly in AL patients with cardiomyopathy.
28.7.2. sFLC response and renal outcome
Pinney et al.  assessed the value of the sFLC response in predicting long-term renal outcome in 923 patients with renal AL amyloidosis. Patients who achieved a greater sFLC response after chemotherapy demonstrated prolonged survival and superior renal outcomes. Patients who achieved more than a 90% FLC response at 6 months had an almost four-fold increase in the chance of renal response (p<0.001) and a lower rate of renal progression (p<0.001) compared with those achieving a FLC response of 0 - 50%. Among 752 patients with a baseline estimated glomerular filtration rate (eGFR) of ≥15 mL/min, those who achieved a 50 to 90% reduction or more than a 90% reduction in dFLC were less likely to experience renal progression requiring dialysis than patients achieving a <50% reduction in dFLC.
It should be noted that in cases of renal insufficiency, use of a modified renal reference interval for the κ/λ sFLC ratio may be appropriate. Application of this reference interval has been demonstrated to improve the diagnostic specificity of the sFLC ratio without affecting diagnostic sensitivity in patients with renal impairment (Section 6.3).