Plasma kinetics of 125I-labelled amyloid P component in β2M amyloidosis: A possible approach to quantitate disease activity

Dialysis amyloidosis is one of the most incapacitating complications of long-term dialysis treatment. Quantitative assessment of amyloid deposition using radiolabelled tracers has been recently proposed but convincing evidence of its validity in uraemic patients remains to be provided. We studied the plasma kinetics of i.v. administered 125I-labelled serum amyloid P component (125I-SAP) in 20 chronic haemodialysis patients compared with those of nine healthy volunteers and three non-dialysed patients with systemic amyloidosis. Plasma clearance of the tracer was abnormal in 17 of 20 dialysis patients in whom plasma radioactivity declined in a bi-exponential mode, in contrast to the single-exponential slope observed in all healthy controls. 125I-SAP plasma half-life of the second component, probably reflecting metabolic clearance, was significantly prolonged in these dialysis patients compared with the healthy controls (35.3 versus 24.6 h, P