SQL & PL/SQL

I'm trying to identify suspect names in our database. One of the tests is to look for values in columnA that do not contain uppercase values. That is, all names in our database should have at least one capital letter. Is there a more efficient way to run the following?

SELECT columnA
FROM mytable
WHERE columnA not like '%A%' 
           and columnA not like '%B%'
           and columnA not like '%C%'
           ... (repeat for D-Y)
           and columnA not like '%Z%'