Ultrastructural examination of urinary sediment. Value in renal amyloidosis.

Examination of urinary sediment has been recommended as a useful diagnostic aid for renal amyloidosis. This procedure was evaluated in the cases of 57 patients, including 11 with proven renal amyloidosis and 13 considered very likely to have the disease. At least three types of urinary fibrillar material were observed: 10-12-nm-diameter fibrils similar to amyloid; 7-10-nm-diameter fibrils with characteristics of intracellular tonofibrils; and 15-30-nm-diameter fibrils suggestive of fibrin tendrils. Only four of 24 patients who had renal amyloidosis proven or suspected had amyloid-like fibrils in the urinary sediment, while four control patients, including three with diabetic nephropathy, had similar fibrils. Sixty-eight per cent of all urines contained material consistent with tonofibrils. Ultrastructural examination of urinary sediment as a diagnostic aid for renal amyloidosis lacks sensitivity and specificity and has very limited clinical value.