Cannot retrieve the table index using get_row

I have a custom table – user_registrations – in my wordpress database which is updated via a plugin.
All the data in the table is completely available and displayable to me using get_row as follows:

$loop_count = 0;
					
//*****
//***** set up the query and retrieve all records from the user table corresponding to this email address		
$sql_query = $wpdb->prepare ("SELECT * FROM user_qualifications WHERE user_contact_email=%s AND user_status=%s ORDER BY user_registration_id", $current_user->user_email, "Submitted") ;
$row = $wpdb->get_row($sql_query, OBJECT, $loop_count);
								
while ($loop_count < $record_count) {

... some other code

	echo "<td><p>" . addslashes($row->user_ridername) . "</p></td>" ;
	echo "<td><p>" . addslashes($row->user_horsename) . "</p></td>" ;
	echo "<td><p>" . $row->user_discipline . "</p></td>" ;
	echo "<td><p>" . $row->user_qualifying_class . "</p></td>" ;
	$submitted_date = $row->user_submitted_date ;
	$submitted_date = date("d-m-Y", strtotime($submitted_date)) ;			   		
	echo "<td><p>" . $submitted_date . "</p></td>" ;
	echo "<td><p>" . addslashes($row->user_showground) . "</p></td>" ;
	echo "<td><p>" . $row->user_index . "</p></td>" ;

etc...

Although all the other fields are output correctly, the field ‘user_index’ just comes out blank. I can’t assign it to a variable and print that either.

The user_index field is the primary key for the table, and displays fine in phpmyadmin. It’s an auto incrementing field of type BigInt.

What am I missing? Is there another way to get this data?