Immunofixation Electrophoresis Was Highly Specific for the Diagnosis of Renal Light-Chain Amyloidosis

BackgroundRenal light-chain amyloidosis (AL)1is one of the common causes of massive proteinuria and nephrotic syndrome, especially in elderly patients. This study aimed to evaluate the sensitivity and specificity of serum and urine using immunofixation electrophoresis (IFE) in the diagnosis of renal AL amyloidosis in patients older than 40 years.MethodsPatients receiving native renal biopsy in the hospital who meet the following criteria were recruited in this retrospective study: (1) proteinuria excretion ≥ 3.5 g/24 hr; (2) age ≥ 40 years when receiving renal biopsy and (3) biopsy-proven glomerulopathy. Serum and urine monoclonal free immunoglobulin light chains were detected using IFE.ResultsA total of 625 patients were recruited. Of them, 32 patients (5.12%) were diagnosed as renal AL amyloidosis. The specificities of serum, urine and serum combined urine IFE in the total 625 patients (ie, monoclonal free immunoglobulin light chain in serum or urine) for diagnosis of renal AL amyloidosis were 98.6%, 98.0% and 97.6%, respectively. For patients older than 60 years, the specificities of serum, urine and serum combined urine IFE for diagnosis of renal AL amyloidosis were 98.5%, 98.0% and 97.6%, respectively and the sensitivity of serum, urine and serum combined urine IFE for diagnosis of renal AL amyloidosis were 68.6%, 81.3% and 81.3%, respectively.ConclusionSerum or urine IFE was highly specific for renal AL amyloidosis for patients older than 40 years with nephrotic-range proteinuria. In older patients (> 60 years), both the sensitivity and specificity of IFE for renal AL amyloidosis were high. Combination of serum and urine IFE could improve the sensitivity with comparable specificity.