$re = '/2845CT;([^,]+)/';
$str = '2810X000000466,,APQ4LA805C34REUGJU,2845AP;2810X000000467,,4985,2845ER;2810X000000468,,361301760100,2845CT;2810X000000469,,DV361301760100,2845NC;2810X000000470,,APQ4LA805C34REUGJU,2845NA;2810X000189003,,BC,2845PS;2810X000267245,,E00137336,2845OA;2810X000267246,,E01027004,2845LS;2810X000267247,,E02005628,2845MS;2810X000331704,,C,284599;2810X000384460,,01/04/1993,284591';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php