U Test in Instrument Regression

[Maximiser John]

Dear Fellow members,

I have a small question can I use U shape test also similar in IV regression than in simple OLS? Bewlo how I would use it (it is not simple IV but zeroth stage adjusted)

reg pdiv_aa mdist_rescaled ${geovars} ${contall} ${ethfrac} ${ethpolr} if smpl_flag1 == 1, robust
predict pdiv_aa_hat if smpl_flag1 == 1, xb
gen pdiv_aa_hat_sqr = pdiv_aa_hat ^ 2
ivreg2 mean_total_100 (pdiv_aa pdiv_aa_sqr = mdist_rescaled pdiv_aa_hat_sqr) ${geovars} ${contall} ${ethfrac} ${ethpolr} ${popsize} ${ypercap} if smpl_flag1 == 1, robust first savefirst
utest pdiv_aa pdiv_aa_sqr

Thanks in advance!!