It’s Monday 24 April 2017. Tomorrow is Anzac day, a day that Australians and people from New Zealand hold dear as we remember brave warfighters who fought and fell in battle to ensure our personal freedom.
Tonight, I want to venture a little out of my area of knowledge into a couple of other disciplines of pathology, namely, hæmatology and chemical pathology.
The subject matter though are two tests we use as indicators of acute phase inflammation. One is a very old test and the other is old but not that old, by which I mean it’s been used commonly in my life time.
The erythrocyte sedimentation rate or ESR is a hæmatology test that is more than a century old.
The ESR is the rate at which erythrocytes sediment over one hour. It is a nonspecific measure of inflammation. In the old days, anticoagulated blood would be placed in a vertical tube and the rate of sedimentation of red blood corpuscles would be measured. These days the test has been automated somewhat.
The rate of sedimentation is a balance between pro and anti-sedimentation factors. The pro factor is mainly fibrinogen while the factors working against sedimentation include the negative charge of the red blood corpuscles. During inflammation, there is a large amount of fibrinogen present which causes erythrocytes to adhere to one another. The corpuscles form dense rouleaux which settle faster.
Here’s a fun fact, did you know that the basal ESR is higher in women?
The ESR is raised in inflammation, pregnancy, anæmia, rheumatoid arthritis and systemic lupus erythematosus, some renal disease and some malignancies. The ESR is reduced when there are too many erythrocytes, hyperviscous blood, sickle cell anæmia, congestive cardiac failure, a low plasma protein and some leucæmias.
These days, the ESR is used to monitor therapy of diseases like temporal arteritis, polymyalgia rheumatica and rheumatoid arthritis. With treatment working you expect the ESR to reduce over time.
C reactive protein is a test performed in chemical pathology. Like the ESR, the CRP is a marker of inflammation. CRP is produced by the liver.
The CRP is raised in burns, trauma, infection, myocardial infarction (or heart attack), chronic inflammatory diseases like rheumatoid arthritis and systemic lupus erythematosus, inflammatory bowel disease and some malignancies.
Unlike the ESR, the CRP can be measured relatively quickly in an automated analyser. It’s also less labour intensive and cheaper to perform. The CRP has now become the standard for looking for acute inflammation.
When we have a positive blood culture in microbiology, we review a patient’s full blood examination and chemical pathology profiles including the CRP to provide an idea of the significance of the bacteræmia. These tests of inflammation are important for gaining a better appreciation of a patient’s position and an example of how medicine is a culmination of factors and not looking as a single test result in isolation.
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