Erythrocyte sedimentation rate, C-reactive protein and plasma viscosity are blood tests that detect inflammation. These are useful tests to help diagnose and monitor the activity of certain diseases.
Inflammation and blood proteins
If you have inflammation in a part of your body then extra protein is often released from the site of inflammation and circulates in the bloodstream. The erythrocyte sedimentation rate (ESR), C-reactive protein (CRP) and plasma viscosity (PV) blood tests are commonly used to detect this increase in protein, and so are markers of inflammation.
Erythrocyte sedimentation rate, C-reactive protein and plasma viscosity blood tests
Erythrocyte sedimentation rate (ESR)
A blood sample is taken and put in a tube that contains a chemical to stop the blood from clotting. The tube is left to stand upright. The red blood cells (erythrocytes) gradually fall to the bottom of the tube (as a sediment). The clear liquid plasma is left at the top. The ESR measures the rate at which the red blood cells separate from the plasma and fall to the bottom of a test tube. The rate is measured in millimetres per hour (mm/hr). This is easy to measure as there will be a number of millimetres of clear liquid at the top of the red blood after one hour.
If certain proteins cover red cells, these will stick to each other and cause the red cells to fall more quickly. So, a high ESR indicates that you have some inflammation, somewhere in the body.
Levels of ESR are generally higher in females and also the level increases with increasing age.
C-reactive protein (CRP)
This is sometimes called an acute phase protein. This means that the level of CRP increases when you have certain diseases which cause inflammation. CRP can be measured in a blood sample.
Plasma viscosity (PV)
The conditions which the ESR test monitors can also be monitored by the PV test. However, it is more difficult to perform and is not as widely used as ESR testing.
What conditions affect the erythrocyte sedimentation rate and C-reactive protein level?
Raised ESR, CRP and PV levels are all markers of inflammation. Generally, PV and ESR do not change as rapidly as CRP does, either at the start of inflammation or as it goes away. CRP is not affected by as many other factors as the PV or ESR, making it a better marker of some types of inflammation. PV, however, is more sensitive and more specific than either ESR or CRP when monitoring the activity of rheumatoid arthritis.
ESR, CRP and PV can be raised in many inflammatory conditions - for example:
- Certain infections (mainly bacterial infections).
- Certain types of arthritis.
- Various other muscular and connective tissue disorders - for example, polymyalgia rheumatica or temporal arteritis.
- Tissue injury and burns.
- Crohn's disease.
- Rejection of an organ transplant.
- Heart attack.
Some conditions lower the ESR - for example, heart failure, polycythaemia, sickle-cell anaemia, and cryoglobulinaemia.
When are these tests used?
To help diagnose diseases
ESR, CRP and PV are nonspecific tests. Basically, a raised level means that "something is going on", but further tests will be needed to clarify the cause of the illness. For example, you may be unwell but the cause may not be clear. A raised ESR, CRP and PV may indicate that some inflammatory condition is likely to be the cause. This may prompt a doctor to do further tests to find the cause.
It is not usually possible to make a diagnosis of a certain condition just from a raised ESR, CRP or PV level.
However, before you have further tests, your doctor may suggest that you have the ESR, CRP or PV test repeated after a period of several weeks or months. If it has been raised by a recent infection (a very common cause) then it is likely to return to normal when your infection improves and you will not then need any further tests.
To monitor the activity of certain diseases
For example, if you have polymyalgia rheumatica, the amount of inflammation and disease activity can partially be assessed by measuring one of these blood tests. As a rule, the higher the level, the more active the disease. The response to treatment may also be monitored, as the level of ESR, CRP and PV may fall if the condition is responding well to treatment.
All three tests are useful. However, changes in the CRP are more rapid. So, for example, a fall in the CRP within days of starting treatment for certain conditions is a useful way of knowing that treatment is working. This may be important to know when treating a serious infection or a severe flare-up of an inflammatory condition. For example, if the CRP level does not fall, it may indicate that the treatment is not working and may prompt a doctor to switch to a different treatment.
Dr Louise Newson
Prof Cathy Jackson