CRP Test vs. ESR Test: Differences and When Each is Used

Inflammation is a normal function of the body, but prolonged inflammation may point to an infection, autoimmune disorder, or other diseases in the body. Blood tests for inflammation are not only an objective indicator of inflammation but also an important diagnostic tool.

The two common tests used in the determination of these values are the C-reactive protein (CRP) test and the erythrocyte sedimentation rate (ESR) test. Both are used to measure inflammation, but they are dissimilar in how they are employed and how they diagnose diseases. In this article, the author shall discuss the differences between the CRP and ESR tests, when each is useful, and in what circumstances.

It is a blood test that calculates the quantity of C-reactive protein in the bloodstream. CRP is a protein that is synthesized in the liver in response to inflammation or injury. It plays the role of the immune system and is used to diagnose infections, injuries, or other diseases that may be chronic in nature.

High CRP levels largely represent the presence of inflammation in the body, which may be caused by infections, autoimmune diseases, and many more. Hence, the CRP test is applied to diagnose and track the improvement or worsening of diseases in which inflammation is a crucial factor, for instance, rheumatoid arthritis, and lupus, among others.

The CRP test is a routine blood test. A healthcare provider uses a needle to collect the sample of blood from a vein usually located on the arm. The sample is then tested on a laboratory analyzer to come up with the CRP value.

There are two variations of the CRP test: the basic CRP test, which measures the middle to high levels of inflammation, and the high sensitivity CRP test used to determine the risks for cardiovascular diseases.

A CRP test is very useful when inflammation is expected in infections, Autoimmune diseases, or inflammation syndromes. Conditions like bacterial pneumonia, lupus, and chronic inflammatory bowel disease (IBD) are some of the uses of this test. Furthermore, the hs-CRP test provides data on the risk of cardiovascular disease in patients.

CRP values are expressed in milligrams per liter (mg/L). The normal levels are those below 10 mg/L; higher levels suggest inflammation, and the degree of increase in the value is associated with the extent of inflammation.

For cardiovascular risk, hs-CRP results are classified into three categories: low risk (<1 mg/L), moderate risk (1-3 mg/L), and high risk (>3 mg/L). However, the elevation of CRP should be in relation to other clinical signs and symptoms to identify the source of inflammation.

The ESR test solely quantifies the rate at which red blood cells descend in a test tube of water. This is because inflammation triggers alterations in the proteins within blood plasma such that red blood cell sedimentation occurs more rapidly.

It is suggested that the ESR test reflects inflammatory response and can be informative in the detection of inflammatory conditions, certain infections, or cancers. This is mostly employed in the assessment of the intensity of chronic inflammatory diseases, including rheumatoid arthritis and temporal arteritis.

ESR tests require the patient’s blood to be well mixed in a long, narrow tube to enhance the settling time of the blood sediment. The speed at which these red blood cells drop (the sedimentation rate) is normally expressed in millimeters per hour (mm/hr). An elevated sedimentation rate shows that there is inflammation within the body because red blood cells settle faster when the protein called fibrinogen, which is associated with inflammation, is present in the bloodstream.

An ESR test is typically requested by a physician if a patient exhibits signs of having a chronic inflammatory disorder such as rheumatoid arthritis, lupus, or specific forms of cancer. It can, therefore, also be used to track the progression of such conditions over time. Temporal arteritis, polymyalgia rheumatica, and some infectious diseases are some examples where an ESR test is commonly used.

ESR increases with age and gender; however, the normal ranges are less than 15 mm/hr for males below 50 years and below 20 mm/hr for females below 50 years. Higher levels indicate inflammation; however, similar to the CRP test, the ESR test is also a marker with no specific indication. It signals the body’s inflamed state but does not specify the root of inflammation. Hence, an elevated ESR result generally indicates that more tests need to be conducted to identify the actual cause.

CRP and ESR tests give different information about inflammation in the body. CRP is an index that reflects the amount of a certain protein (C-reactive protein) that is produced in the liver in response to inflammation. ESR represents the speed at which the red blood cells precipitate in the test tube. It is dependent on proteins in the blood that rise in inflammation. CRP is a more acute phase reactant protein in contrast to ESR, which is a more generalized indicator of acute and chronic inflammation.

CRP is a better marker of changes in inflammation than ESR, particularly in the acute phase of the disease. Elevated levels of CRP are apparent soon after the inflammation commences and dissolve quickly as soon as the inflammation ceases. While ESR is affected by inflammation, the change is relatively slower and less distinct, thus making it ideal for conditions that require a long-term assessment.

CRP is usually elevated within several hours after an inflammatory process and rapidly declines as soon as inflammation subsides. ESR levels, however, are slower in rising and falling and can take days to weeks to come down even after the inflammation has started subsiding. This makes CRP more sensitive to changes in inflammation and can be used to quickly evaluate the worsening or improvement of inflammation, while ESR is more suitable for chronic inflammations.

CRP is typically utilized when a rapid measurement of inflammation is required, for example, in bacterial infection, sepsis, or estimation of cardiovascular risk. ESR, due to its slower response time, is often used in chronic inflammatory conditions such as rheumatoid arthritis or temporal arteritis, where the goal is to monitor long-term disease activity.

When doctors want to check for inflammation, they can use two tests: CRP and ESR. The choice of test depends on the patient’s situation.

The CRP test is good to help with acute inflammation. This means it helps when there is a sudden problem, like an infection. For example, if a patient has pneumonia, doctors use the CRP test. It can show if there is a lot of inflammation quickly. It helps doctors decide on the best treatment right away.

The ESR test is better for chronic conditions. Chronic conditions last a long time, like arthritis or lupus. The ESR test shows how much inflammation is in the body over time. It helps doctors see if a treatment is working or if the disease is getting worse.

Sometimes, doctors order both tests. This gives a fuller picture of what is happening in the patient’s body.

We can say that CRP and ESR tests are important for checking inflammation. CRP is fast, and it helps to find acute problems like infections. On the other hand, ESR is slower but helps with long-lasting conditions.

Doctors can choose the best test according to each patient's condition. Patients should ask their doctors which test is right for them. Thus, they can get the best care possible. Both tests help doctors monitor health and make better treatment decisions.

* * Medical Disclaimer - The following information is for educational purposes only. No information provided on this website, including text, graphic, and images, are intended as substitutes for professional medical advice. Please consult with your doctor about specific medical advice pertaining to your condition(s).