Bubble cells: renal tubular cells in the urinary sediment with characteristics of viability.

The urinary sediment was examined by light microscopy in 65 consecutive inpatients with renal insufficiency (not due to pre- or postrenal factors) referred to a nephrology consult service for evaluation. In the 60 patients in whom a single diagnosis was reached, the sediments of 34 (57%) contained an easily recognized cell, which we have called the "bubble cell". These cells were bizarre, large cells with a single nucleus, which appeared to contain one or more fluid-filled vesicles. Bubble cells were most prevalent in the sediment of patients with acute tubular necrosis but were also seen a variety of other renal diseases. In most patients with acute tubular necrosis, the sediment also contained "normal"-appearing renal tubular cells, muddy brown casts, and oval fat bodies which were indistinguishable from those seen in the nephrotic syndrome. By electron microscopy, the bubble cells appeared to be vacuolated renal tubular epithelial cells, which had characteristics of viable cells. Most bubble cells excluded the vital dye Trypan blue, whereas the normal-appearing renal tubular cells were typically strongly positive. It was concluded that bubble cells, often accompanied by oval fat bodies, are commonly present in the sediment of patients with acute tubular necrosis as well as many other types of renal disease. Most cells which would be classified as "normal" renal tubular cells in these sediments are dead. In contrast, the findings suggest that the bubble cell represents an injured but viable renal tubular cell. The frequent finding of oval fat bodies in the same sediments suggests that the oval fat body is also produced by tubular cell injury.