Abstract

To the Editor:

Aycock and Kass pointed out in their review article regarding abnormal urine color, published in the January 2012 issue of theSouthern Medical Journal,¹ that any abnormal discoloration of the urine, although typically benign, can be distressing for patients and relatives as well as puzzling to healthcare professionals. Therefore, knowledge of the various causes of urine discoloration as summarized in the manuscript figure is useful. I would like to point out, however, a mistake made in the section on purple urine. Aycock and Kass state that the cause of purple urine bag syndrome is purple urine. We have encountered this condition several times and, in fact, the urine in purple urine bag syndrome is not purple but usually dirty brownish-red.² The responsible pigments, indirubin (red) and indigo (blue), do not discolor the urine directly, but, after reacting with the lining of the urine bag and catheter, precipitations occur to form the purplish discoloration. Bluish discoloration can be seen occasionally and attributed to the imbalance of these two pigments. Therefore, in purple urine bag syndrome, the urine bag itself is discolored purple, not the urine.