Listing Output from Two 'Category' Fields

On my website I have a simple category system, which consists of a text field called 'category' and that contains a text list of different categories (e.g. "Cars", "Trucks and Vans" etc.). Now when I want to output which categories apply to a particular product then I usually do this:

  <!-- STEP2: Display Records (Paste this where you want your records to be listed) -->
    <?php foreach ($isp_listRecords as $record): ?>
<li><a name="<?php echo $record['num'] ?>"></a><b style="line-height:22px;color:#716f64;font-size: 14px;"><?php echo $record['title'] ?></b> (<?php echo $record['location_hq'] ?>)<br />-- <?php 
$numx = $record['num'];
$test = $record['title'] = preg_replace("/[ ]/", "-", $record['title']);
$test2 = "-";
$replace = array();
$replace['Cars'] = "<a href=ISP_Detail_Cars.php?"."$test$test2$numx".">"."Cars"."</a>";
$replace['Trucks and Vans'] = "<a href=ISP_Detail_Trucks.php?"."$test$test2$numx".">"."Trucks and Small Vans"."</a>";
$text = join(', ', getListLabels('isp_list', 'category', $record['category']));
foreach ($replace as $k=>$v)
{
   $text = str_replace($k, $v, $text);
}
echo $text;
?></li><br />

    <?php endforeach ?>
</ul>

    <?php if (!$isp_listRecords): ?>
      <br /><br /><b><u>No records were found!</u></b><br/><br/>
    <?php endif ?>
  <!-- /STEP2: Display Records -->

Generally this works fine, but recently my products database has become more complicated and I've needed to create a second 'category2' field to add a particular sub-set of products (e.g. "Modified Trucks"). Now I'd like to output the "Modified Trucks" category using the same code above, so I need to check against both the data / category lists inside fields 'category' and 'catergory2' and I think that requires me to edit this line:

$text = join(', ', getListLabels('isp_list', 'category', $record['category']));

Any ideas how I can tweak this so I'm searching / checking against categories for both the 'category' (already used above) and the new 'category2' field?