Cross-Matching Explanation

Further to the previous post, I've now had a sensible explanation for the need for cross-matching blood immediately before the operation: it's to identify suitable blood for possible use during the operation as a transfusion.  If they don't do this beforehand then, in an emergency, they would have to use blood which was "probably" the right match but may not be the best match; the analysis takes a few hours and in an emergency they don't have that time to spare! Obvious really, innit? Why can't people tell you the simple answer in a simple fashion?

Possibly there might also be a cross-match with Tim's blood but, as was explained to me, this is more of a formality as there is no likely reason for either of us to have suddenly produced antibodies, both being blood group O (universal donor).

Anyway, we're off in a couple of hours to London to avoid the morning traffic tomorrow - I wouldn't want to be late for admission at 10am due to the feared London rush hour (which seems to last all day these days), and neither would I want to leave here at 6am.