In our recent AJKD article that described validation of a novel method for monitoring hemodialysis Kt/V, we concluded that, “[i]n addition to greatly reducing the need for postdialysis SUN [serum urea nitrogen] measurements, the new method has the additional benefit of avoiding well-known problems related to improper sampling or measurement of postdialysis SUN.”1,p30 The word “avoiding” here was an overstatement. In the proposed method, the postdialysis SUN is still needed during the baseline period to obtain a “calibration” modeled volume.