(by reading the positing guidelines, you would know that it is extremely complex to help when one example is provided)
Anchor the first word to the beginning of the buffer
´/^[A-Z]{4}\b/´
This will not select anything else that the first word at the very beginning of the buffer, if it exists
If there are spaces, tabs, leading \n\r, any combination of the above, between the beginning of the buffer and the word you want to select, use \s
If there are spaces, tabs, leading \n\r, any combination of the above, between the beginning of the buffer and the word you want to select, use \s´/^\s*[A-Z]{4}\b/´
Does it solve your problem ?