write_gct adds in the index column #80

I'm using write_gct to output a GCT file. GCT files normally have the following columns: name, description, sample1, sample2...

But when I use write_gct, it has the following columns: id, name, description, sample1, sample2...

I've tried dropping the index column from my dataframe, but that doesn't fix the problem. My current code is as follows:

       gctoo = GCToo(expression_df)
       write_gct.write(gctoo, output_filename) 

If I was writing the file myself, directly from the Pandas data frame, I would simply use:

expression_df.to_csv(output_filename, sep='\t', index=False)

Unfortunately, there doesn't seem to be an option in write_gct to accomplish this. Any guidance would be appreciated.