Confirmation is a Sacrament of Initiation in which one completes his/her entrance into the Catholic Church as a full member and confesses the Church as the One True Church and making the visible statement that you are going to follow and believe what the Church teaches. Since Lutheranism, or anything other than Catholic for that matter, does not believe all that the Church teaches, and in some cases teaches against what the Church believes, confirmation in such churches does not declare a confession of the Catholic Church as the True Church or that you will follow Church teaching, and therefore does not count. This is one of the “Because it’s not Catholic, it doesn’t count.” things, to put it in simplest terms. In terms of Sacraments (from what I can tell), in most cases no Sacraments except for Baptism and Marriage are considered valid.