use warnings;
use strict;

my @lines = <DATA>;

for my $line (@lines){
  chomp $line;
  if($line =~ m/(^OBX\|)([^\|]*\|)([^\^]*)(.*$)/){
    my ($pre, $read, $post) = ($1 . $2, $3, $4);
    $read =~ s/([a-zA-Z])/($1 lt 'a' ? 'U' : 'L').$1/ge;
    $line = "$pre$read$post";
  }
  print "$line\n";
}

__DATA__
NTE||L|obr note
OBX|NM|aaA..^Haem^RD2|7.5|g/dL|13.0-18.0|OR|
NTE||L|obx note 1/1 for 3058
OBX|NM|dBf..^TWC^RD2|8.9|10*9/L|4.0-11.0||

##</code><code>##

NTE||L|obr note
OBX|NM|LaLaUA..^Haem^RD2|7.5|g/dL|13.0-18.0|OR|
NTE||L|obx note 1/1 for 3058
OBX|NM|LdUBLf..^TWC^RD2|8.9|10*9/L|4.0-11.0||