{"id":802,"date":"2014-09-11T21:54:28","date_gmt":"2014-09-11T21:54:28","guid":{"rendered":"http:\/\/drcrunch.wordpress.com\/?p=802"},"modified":"2014-09-11T21:54:28","modified_gmt":"2014-09-11T21:54:28","slug":"using-the-crp-on-inpatients","status":"publish","type":"post","link":"http:\/\/drcrunch.co.uk\/blog\/2014\/09\/11\/using-the-crp-on-inpatients\/","title":{"rendered":"Using the CRP on inpatients"},"content":{"rendered":"

“Stay in till tomorrow to recheck\u00a0the CRP. If it goes down to less than 100 he goes home.”<\/em><\/p>\n

“It’s day 2 post op.\u00a0The CRP is 167 from 67 the day before. Is that normal or do we look for a possible infection?”<\/em><\/p>\n

“Giant cell arteritis? Use ESR, CRP is useless.”<\/em><\/p>\n

I\u00a0decided to read up on the CRP, focusing on bits that would help make sense of\u00a0the clinical situations\u00a0above.<\/p>\n

1. The half life of CRP is 18-19 hours.<\/strong><\/p>\n

“Stay in till tomorrow to recheck\u00a0the CRP. If it goes down to less than 100 he goes home.”<\/p><\/blockquote>\n

This half life is remarkably constant <\/a>no matter what else is going on, be it renal failure, liver failure, sepsis, polypharmacy etc. This means that the plasma level of CRP is dependent on\u00a0how much<\/em> was made and when<\/em>.\u00a0\u00a0It is only dependent on factors affecting its production, not its elimination.<\/p>\n

Once the insult is removed, CRP should drop toward baseline. It should be normal within two or three days (which corresponds to 3-4 half lives i.e. 7\/8th or 15\/16th eliminated).<\/p>\n

The CRP can therefore lag behind the clinical picture. If the patient is clinically well and has an identifiable insult that has recovered in the last 48 hours, you do not necessarily need to wait for the CRP to come down to ‘prove’ the patient has recovered.<\/p>\n

2. CRP levels usually peaks at about 48 hours after the insult.<\/strong><\/p>\n

“It’s day 2 post op.\u00a0The CRP is 167 from 67 the day before. Is that normal or do we look for a possible infection?”<\/p><\/blockquote>\n

CRP production\u00a0does not happen instantly at the time of the insult; it is delayed by at least 2 hours, and really kicks in at around 6 hours. This means that the CRP would normally<\/em> rise between day 1 and day 2 post op for example.<\/p>\n

3. The CRP goes up with most causes of inflammation.<\/strong><\/p>\n

“Giant cell arteritis? Use ESR, CRP is useless”<\/p><\/blockquote>\n

CRP\u00a0is made pretty much exclusively by the liver as part of the acute phase response. The acute phase response\u00a0includes\u00a0a protein synthesis strategy change by the liver following activation of the innate immune system by something nasty – an infection, autoimmune disease, burns, trauma or maybe a neoplasm. A raised CRP is very sensitive for ‘some inflammation somewhere’ but very unhelpful for determining the aetiology.<\/p>\n

The most famous\u00a0exception is SLE, where CRP often stays normal whilst the disease flares. Interestingly, the SLE patient still mounts a CRP rise in response to infection. This means that measuring CRP during a suspected flare can help distinguish between an autoimmune flare or an infection.<\/p>\n

A normal ESR is seen in 8-22.5%<\/a> of cases of giant cell arteritis. In contrast, an elevated CRP is thought to be near 100% sensitive for the condition. You can have an elevated CRP with a normal ESR <\/a>in GCA. However, it is ESR rather than\u00a0CRP that\u00a0is used in the diagnostic criteria <\/a>for GCA.<\/p>\n","protected":false},"excerpt":{"rendered":"

“Stay in till tomorrow to recheck\u00a0the CRP. If it goes down to less than 100 he goes home.” “It’s day 2 post op.\u00a0The CRP is 167 from 67 the day…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"spay_email":"","footnotes":"","jetpack_publicize_message":""},"categories":[1],"tags":[],"class_list":["post-802","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"jetpack_featured_media_url":"","jetpack_publicize_connections":[],"jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p9zRNY-cW","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"http:\/\/drcrunch.co.uk\/blog\/wp-json\/wp\/v2\/posts\/802","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/drcrunch.co.uk\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/drcrunch.co.uk\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/drcrunch.co.uk\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/drcrunch.co.uk\/blog\/wp-json\/wp\/v2\/comments?post=802"}],"version-history":[{"count":0,"href":"http:\/\/drcrunch.co.uk\/blog\/wp-json\/wp\/v2\/posts\/802\/revisions"}],"wp:attachment":[{"href":"http:\/\/drcrunch.co.uk\/blog\/wp-json\/wp\/v2\/media?parent=802"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/drcrunch.co.uk\/blog\/wp-json\/wp\/v2\/categories?post=802"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/drcrunch.co.uk\/blog\/wp-json\/wp\/v2\/tags?post=802"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}