use strict;
use Data::Dumper;
use DBI qw(:sql_types);
use Tie::IxHash;

tie my %results, "Tie::IxHash";

... connect to db ....

my $stmt = qq~SELECT * FROM registrants WHERE registrant_id = ?~;
%results = % { $dbh->selectrow_hashref($stmt, undef, $registrant_id) };