Unmasking amyloid light-chain amyloidosis through biochemical lens: diagnostic utility of urine immunofixation in serum-negative cases

This case underscores the diagnostic challenges of AL amyloidosis, particularly in serum-negative presentations with low tumor burden. Role of UIFE was pivotal in detecting monoclonal lambda light chains excreted via the kidneys, overcoming the limitations of serum-based assays. The absence of serum monoclonal proteins in early-stage disease mandates a multimodal approach: integrating clinical suspicion (e.g., nephrotic syndrome, cardiomyopathy, or neuropathy in older adults), urine studies, serum FLC assays, and targeted biopsies.