How to insert a css class from the custom field in a url?

Created a custom field “class” with the value “dsbld”.
There is a page with links to posts. How in the loop check custom field and assign to the link class=”dsbld”?

url code:

<a href="'.get_permalink($udt_project->ID).'" title="'.esc_attr($udt_project->post_title).'">

All block code:

$display_media_size='aggressive-thumb';
					if (has_post_thumbnail($udt_project->ID)) {
						$project_thumbnail_id = get_post_thumbnail_id( $udt_project->ID );
						$image_src=wp_get_attachment_image_src($project_thumbnail_id, $display_media_size);
						$display_media_caption='';
						if(isset($udt_portfolio_meta['display_media_caption']) && $udt_portfolio_meta['display_media_caption']!='') {
							$display_media_caption=$udt_portfolio_meta['display_media_caption'];
						}
						$display_media_caption_small = '';
						if(isset($udt_portfolio_meta['display_media_caption_small']) && $udt_portfolio_meta['display_media_caption_small']!='') {
							$display_media_caption_small=$udt_portfolio_meta['display_media_caption_small'];
						}
						echo '<div class="thumb" data-project-categories="'.$project_categories.'">
							<a>ID).'" title="'.esc_attr($udt_project->post_title).'">
								<div class="thumb_img"><img src="'.$image_src[0].'" alt="'.esc_attr($udt_project->post_title).'"></div>
								<div class="thumb_text">'.$display_media_caption.'<span>'.$display_media_caption_small.'</span></div>
								<div class="thumb_caption">'.esc_attr($udt_project->post_title).'</div>
							</a>
						</div>';
					}