Which Lieutenant is Renji not counting?
At the time the 13th Division did not have a vice captain. After Kaien Shiba's death sometime before the start of the series, the position goes a while unfilled, with the duties being covered by the two third seats of 13th division, before passing on to Rukia. Therefore there was no vice captain at the time Ichigo came to rescue Rukia.

http://bleach.wikia.com/wiki/13th_Division