  Using recent results of Avdeev et al. and an expansion for $\mu_t/\mms$
($M_t$ is the pole mass and $\mu_t\equiv \hat{m_t}(\mu_t)$ ), it is shown that
when deltarho is expressed in terms of $\hat{m_t}^2(M_t)$, the QCD correction
is only $(2-3)\times 10^{-3}$ in the NLO approximation. As a consequence, in
terms of $M_t^2$ the correction to $\dr$ is almost entirely contained in
$\mmss/M_t^2$, a pure QCD effect.
  The latter is studied using various optimization procedures, and the results
compared with the expansion proposed by Avdeev et al.. Implications for \ew
physics are discussed. Threshold effects are analyzed on the basis of a simple
sum rule.
