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To assess the diagnostic accuracy and additional information provided by ¹²³I-labeled serum amyloid P component (SAP) scintigraphy in patients with systemic and localized amyloidosis.

¹²³I-labeled human SAP was injected intravenously into 20 controls and 189 consecutive patients with histologically proven amyloidosis: of AA type in 60 cases, AL type in 80, hereditary ATTR type in 27, and localized amyloidosis in 22 cases. SAP scintigrams were obtained 24 hours after tracer injection and were analyzed for abnormal patterns of uptake. Sensitivity and specificity were determined, and scintigraphic findings were compared with clinical data.

Diagnostic sensitivity of SAP scintigraphy for systemic AA, AL, and ATTR amyloidosis was 90%, 90%, and 48% respectively, and specificity was 93%. The distribution of amyloid was less diverse in AA than in AL type …