compare c-index of two logistic models using rcorrp.senc() of the Hmisc library

Dear R-help,

Would it be appropriate to do the following to
calculate a p-value for the difference between c-ind
of x1 and c-inx of x2 using the output from
rcorrp.senc()

r<-rcorrp.senc(x1,x1,y)

pValue<-1-pnorm((r[11]-r[12])/(r[2]/r[5])*1.96) 

Osman O. Al-Radi, MD, MSc, FRCSC
Chief Resident, Cardiac Surgery
University of Toronto, Canada