Information about inflammation
This month, we continue our new series about the most common diagnostic tests. Here Prof. Shyam Fernando, a consultant physician and Professor in Medicine looks at CPR and ESR, among the most common blood tests. Read on to discover what these tests actually entail, how they are applied and what role they play in allowing the doctor to reach a diagnosis. Also understand your role – how should you prepare? What after effects should you be braced for?
What they are:
The three letters ‘ESR’ stand for Erythrocyte Sedimentation Rate. It measures how much of inflammation is going on in your body. It is a ‘screening test’. It is not used to identify any specific disorder. A ‘screening’ in medical jargon means looking for diseases before they become apparent. The ESR is done in some unexplained fevers, suspected cases of arthritis and infections. After making a diagnosis of a disease, the ESR helps the doctors monitor the disease activity, to see whether it is responding to treatment or flaring up.
CRP or C-reactive protein is, just like the ESR, a blood test that tells us how much of inflammation is going on in your body. This protein is produced in the liver. It has nothing to do with your level of nutrition or how much of proteins you eat. Though it measures the same thing as the ESR does, it is more sensitive than the ESR to inflammation.
How are they done:
It is done on a sample of blood taken into a special bottle, by pricking your arm vein. In the lab, blood is put into a tall thin tube, which is kept standing for one hour. The lab technicians measure how fast it takes for the red cells (erythrocytes) to fall to the bottom and sediment is measured. This is the ‘sedimentation rate’.
How are they used in diagnosis?
The ESR is notably high in blood cancers such as myeloma, joint problems such as rheumatoid arthritis and in most bacterial infections particularly bone infections, heart valve infections (endocarditis) and tuberculosis.
The normal value varies between 10 to 30 millimetres per hour (mm/hr). Older people tend to have a higher ESR than the younger ones. ESR is generally higher in women than in men. In pregnancy, it is even higher. The normal values might vary among different labs.
An abnormal ESR does not always mean you have a specific illness. Other tests are needed to find out why the ESR is high. It only helps the doctor in diagnosis and following up diseases. Your doctor might even ignore an insignificant abnormality!
CRP level is high in most of the conditions where ESR is also high. However, because it is more sensitive, it rises earlier than the ESR when the inflammation sets in. Once the disease starts responding to treatment, CRP level starts falling long before the ESR does. So, CRP is better than the ESR for keeping track of fast changes.
There is a long list of conditions where the CRP is high. The normal values may vary from lab to lab. The significance of a raised CRP has to be determined by your doctor only after taking into consideration your clinical history.
How do I prepare?
No preparations. Just walk in.
What are the after-effects?
None. Just a little pain at the site of prick. Occasionally a bit of blood can ooze out and get collected under the skin (haematoma).
What are the pitfalls?
A high ESR does not mean you have a fatal condition. So, don’t panic. Your doctor will read the result along with other information (your clinical history, examination findings) and decide what should be done. He might order other tests to find out why the ESR is high. A slightly abnormal result for no apparent reason is also not unusual. Don’t expect the ESR to be exactly the same every time it is done. We are not factory-made robots!