Full example, tracking WordPress category into Google Analytics custom variable

ga-custom-page-level.js

<script type="text/javascript">

var _gaq =_gaq || [];
 _gaq.push(['_setAccount', 'UA-XXXXXXXX-X']);

if (is_single () ) {

$category = get_the_category();
echo "_gaq.push(['_setCustomVar', 2,'Category','". $category[0]->cat_name. "', 3]);";

} else {

}

_gaq.push(['_trackPageview']);
_gaq.push(['_trackPageLoadTime']);

(function() {

 var ga = document.createElement('script');
 ga.type = 'text/javascript';
 ga.async = true;

 ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js';
 var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga,s);
})();

</script>