10 May 2022
Jessica Watson is a GP who has done a PhD on inflammatory marker blood tests. In this blog she answers commonly asked questions about these blood tests.
Inflammatory markers are blood tests used by doctors to detect inflammation in the body, caused by many diseases. This can include infections, auto-immune conditions and cancers. The three most commonly used inflammatory markers are called C-reactive protein (CRP), erythrocyte sedimentation rate (ESR) and plasma viscosity (PV).
CRP, PV and ESR each measure inflammation in the blood in slightly different ways.
The body produces proteins as part of the normal response to infection or inflammation. One of these proteins is call C-reactive protein (CRP). CRP is released quickly at the start of infections or inflammatory conditions.
Plasma viscosity is another test which measures the thickness (or ‘viscosity’) of blood. This is done by calculating the force needed to send plasma (the liquid part of blood) down a thin tube in a given time. During inflammation this thickness (or viscosity) increases because lots of different protein levels rise in the blood.
Erythrocyte sedimentation rate also gives doctors an indication of the amount of protein in the blood, by measuring the fall (sedimentation) of erythrocytes (red blood cells) in a tube of blood. Increased levels of protein cause red blood cells to fall more rapidly, increasing the ESR.
Generally, PV and ESR do not change as rapidly as CRP. CRP is not affected by as many other factors as PV or ESR.
Inflammatory marker tests are all non-specific tests. This means they don’t identify what’s causing the inflammation: it might be as simple as a mild infection, or as serious as cancer.
Inflammatory markers can be useful in helping to diagnose or monitor inflammatory conditions. These include:
When a doctor suspects one of these conditions, a raised inflammatory marker can help them to make the diagnosis.
If you are already diagnosed with one of these conditions, your doctor may use inflammatory marker tests to monitor response to treatment or to identify when you have a flair up.
Sometimes doctors use inflammatory markers as a non-specific test to rule out serious disease. If inflammatory marker tests are done without a clear reason it can sometimes be difficult to know what the results mean.
Medical decisions will not be made solely on the results of an inflammatory marker test. Abnormal results suggest inflammation, but don’t identify the cause: it might be as simple as a viral infection, or as serious as cancer. Having a raised inflammatory marker doesn’t always mean you have a disease, they can also be raised in people who are overweight; ESR is also affected by age, gender, smoking and anaemia. It’s also important to know that a normal inflammatory marker test result does not exclude illness.
A doctor will take into account your symptoms and other test results when reading the results of your blood tests. If you have symptoms that suggest a specific condition, a raised inflammatory marker might be enough to diagnose that condition. This is the case for diseases such as polymyalgia rheumatica and temporal arteritis, which are often diagnosed based on typical symptoms and a raised inflammatory marker blood test.
If the cause of a raised inflammatory marker is not obvious, your doctor may do more tests to try to find the cause. Before doing lots more tests, a doctor may want to repeat the test. Sometimes the results go back to normal on their own and doctors never find a cause for the inflammation.
If you already have an inflammatory disease then rising inflammatory markers may suggest a flair up or a poor response to a treatment; a decreasing inflammatory marker can mean a good response to treatment.
To find out more about this study, take a look at the project summary.