I have spent the past 1 month on the renal consult service at the Brigham. And, after nearly 25 years as a nephrologist I can still struggle with a urine sediment. An example: distinguishing a renal tubular epithelial cell cast from a white cell cast. Take a look at the two casts above and tell me which one is the white cell cast and which one the renal tubular epithelial cell cast. Not so easy!