Why Does Your Rheumatologist Check ESR and CRP?
1/26/26
Many chronic rheumatic diseases are driven by inflammation. Inflammatory processes most commonly affect the joints, but they can also involve other organs such as the skin, lungs, kidneys, blood vessels, and more.
So how do we know if inflammation is present—and how do we measure whether your treatment is working?
This brings us to two commonly checked blood tests: the erythrocyte sedimentation rate (ESR), often called the “sed rate,” and C-reactive protein (CRP).
What is ESR?
ESR measures how quickly red blood cells settle to the bottom of a test tube over one hour. When inflammation is present, certain proteins cause red blood cells to clump together and fall more quickly, resulting in a higher ESR. ESR is an indirect marker of inflammation and can be influenced by age, anemia, and other non-inflammatory factors.
What is CRP?
CRP is a protein produced by the liver in response to inflammation. When inflammation increases anywhere in the body, CRP levels rise—often quickly. Because CRP responds rapidly to changes in inflammation, it is especially useful for monitoring disease activity and response to treatment.
When I teach medical students and residents, I explain that in textbook scenarios, ESR and CRP are elevated when inflammation is active. As treatment is initiated and inflammation improves, these values typically decrease—helping us recognize disease control or remission.
For example, when rheumatoid arthritis (RA) is active, patients often experience joint pain, stiffness, and swelling, and ESR and CRP are frequently elevated. As treatment reduces inflammation and symptoms improve, these labs often normalize.
One advantage of ESR and CRP is that they can be checked frequently—even weekly when needed—making them helpful tools for monitoring disease activity over time.
Can You Have Normal ESR and CRP and Still Have Inflammation?
Yes.
Although ESR and CRP are important tools, they are not perfect. They do not replace clinical judgment.
Some patients have clear signs and symptoms of inflammation—such as persistent joint pain, stiffness, swelling, fatigue, or other systemic symptoms—while their ESR and CRP remain normal. This is why your symptoms and physical examination are so important.
I carefully study your symptoms, examine you, and trend your labs over time to make a clinical assessment based on the full picture—not just a single lab value. This is why I always encourage my patients to know their bodies and share any new or persistent symptoms.
Other Ways to Measure Inflammation
In some cases, we use advanced imaging to detect inflammation. MRI is particularly helpful for identifying soft-tissue and joint inflammation.
For certain conditions, such as large-vessel vasculitis (for example, giant cell arteritis), imaging tools like PET scans, ultrasound, and MRI are increasingly used to identify active inflammation.
Why Is Measuring Inflammation So Important?
The more accurate data we have, the better we can tailor your treatment plan and ensure you are receiving the right therapy at the right time.
What Else Can Elevate ESR or CRP?
Elevated inflammatory markers are not specific to rheumatic disease. Other causes include:
Infections (from mild viral illnesses to serious bacterial infections)
Malignancy (cancer)
Persistently elevated ESR or CRP should always be evaluated thoroughly to identify the underlying cause. Seeing a rheumatologist is appropriate in this situation.
What If I Feel Well but My ESR or CRP Is Elevated?
This does happen. ESR and CRP are not universally reliable, and some patients feel completely well despite abnormal labs. In these cases, we perform a careful evaluation, consider all possible causes, and may monitor the labs over time. Management is individualized.
Should I Automatically Worry About an Elevated ESR or CRP?
In most cases, elevated inflammatory markers are not an emergency, but they do warrant evaluation. This often includes consultation with a rheumatologist. Always keep your doctors informed of new or changing symptoms, as this context is critical when interpreting lab results
Should I Automatically Worry About an Elevated ESR or CRP?
In most cases, elevated inflammatory markers are not an emergency, but they do warrant evaluation. This often includes consultation with a rheumatologist. Always keep your doctors informed of new or changing symptoms, as this context is critical when interpreting lab results
What If My ESR Is Over 100?
An ESR greater than 100 is concerning and requires prompt evaluation. Serious conditions such as:
Severe infections (e.g., septic arthritis, endocarditis, osteomyelitis)
Systemic vasculitis
Certain cancers
can cause markedly elevated inflammatory markers and must be ruled out.
What Should I Do If My ESR or CRP Is Abnormal?
Pay attention to your body and report symptoms such as:
Joint pain, stiffness, or swelling
Fatigue
Fevers or weight loss
Rashes or respiratory symptoms
Seeing a rheumatologist can help identify the cause and guide further testing. Early diagnosis leads to better outcomes.
Key Takeaways
ESR and CRP are blood markers of inflammation and may be elevated in rheumatic disease, infection, or malignancy.
These labs are monitored over time to better understand disease activity.
ESR and CRP do not diagnose disease on their own and must be interpreted in clinical context.
An ESR above 100 is serious and requires prompt evaluation.
Rheumatologists specialize in diagnosing and treating inflammatory diseases and are appropriate consultants for persistently elevated inflammatory markers