In systemic light chain (AL) amyloidosis, the amyloid fibrils are derived from immunoglobulin light chains. Kappa or lambda light chains can form fibrils, but lambda chains are overrepresented. The serum/urine biomarker most specific for monitoring AL amyloidosis treatment response is:
- A Serum amyloid P (SAP) component levels
- B Total serum immunoglobulin (IgG/IgA/IgM) concentration
- C Free light chain (FLC) difference (dFLC) — difference between involved and uninvolved light chains ✓
- D Urine Bence-Jones protein by electrophoresis
Explanation
In AL amyloidosis, the amyloidogenic free light chain (lambda > kappa at 3:1 ratio) is produced by a clonal plasma cell population. The 'dFLC' (difference in free light chain = involved FLC minus uninvolved FLC) is the validated haematological response biomarker: a >50% reduction in dFLC indicates haematological response and correlates with organ response and survival. Serum free light chain assay (nephelometry) replaced older urine Bence-Jones protein testing (low sensitivity, requires 24-hour urine). SAP scintigraphy tracks amyloid organ burden but is not a routine treatment monitoring tool. Total immunoglobulin levels are less specific as they include polyclonal and other paraproteins. dFLC is included in the Consensus Response Criteria for AL amyloidosis.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.