<prompt> The best investigation for the diagnosis of amyloidosis isColonoscopyRectal biopsyUpper GI endoscopyCT scan  <response>: Diagnosis Microscopic examination - biopsies from kidney, gingiva, rectum Congo red staining on abdominal fat aspirates Serum urine protein electrophoresis Bone marrow aspiration - to ro plasmacytosis Scintigraphy with radiolabelled serum amyloid P SAP component 