This is an Excel question, not Matlab...see if there's a method that returns the info directly and use ActiveX to invoke it if so. If not, best I can think of directly from Matlab would be to read the data and see how big an array is returned...this only works if know the beginning column and there aren't empty columns...oh, you can use the optional 'raw' output that will return the actual info in cell array and search within it...
There is no Matlab method directly though, as noted its an Excel question if there is a way internally that you can query.
