The Erythrocyte Sedimentation Rate (ESR), often called the Sed Rate, is a common blood test used to detect inflammation or disease activity. This test measures how quickly red blood cells (erythrocytes) settle to the bottom of a vertical tube over one hour. The rate is reported in millimeters per hour (mm/hr). A result significantly above the established reference range suggests an underlying process is occurring. An elevated ESR does not identify the specific cause, but it acts as a general indicator that an inflammatory response is active.
Understanding the Sedimentation Rate Test
The ESR test relies on the interaction between red blood cells and plasma proteins. In a healthy state, red blood cells possess a negative surface charge, causing them to repel one another and settle slowly under gravity. This slow settling results in a lower ESR reading.
When inflammation is present, the liver produces acute phase proteins, such as fibrinogen and immunoglobulins, which circulate in the blood. These proteins are positively charged and neutralize the negative surface charge of the red blood cells. This neutralization allows the red cells to stick together, forming stacks known as rouleaux.
These rouleaux structures are larger and heavier than individual red blood cells, causing them to fall more rapidly. The faster the cells aggregate and fall, the higher the resulting ESR value, which corresponds to a greater degree of systemic inflammation. The test is considered a general marker of the body’s overall inflammatory state because it measures this physical phenomenon rather than the concentration of a single substance.
Medical Conditions Associated with High ESR
A significantly elevated ESR, especially one exceeding 100 mm/hr, is associated with a serious underlying disease process. Causes are broadly grouped into infections, autoimmune disorders, and chronic conditions or cancers.
Infections, whether acute or chronic, frequently cause a rise in the sedimentation rate. Systemic bacterial infections, such as pneumonia or cellulitis, often trigger a rapid increase in acute phase proteins. Localized infections involving deep tissues, like osteomyelitis or endocarditis, also sustain a high ESR.
The ESR is valuable in autoimmune and systemic inflammatory diseases for both diagnosis and monitoring disease activity. Conditions such as Rheumatoid Arthritis (RA) and Systemic Lupus Erythematosus (SLE) involve chronic inflammation leading to persistently elevated rates. The test is also used when evaluating patients suspected of having vasculitides (blood vessel inflammation).
A raised ESR is a diagnostic feature for conditions such as Polymyalgia Rheumatica (PMR) and Temporal Arteritis (Giant Cell Arteritis). In these disorders, the degree of elevation often correlates with inflammation severity, making it a tool for assessing treatment effectiveness. An elevated rate is also observed in Inflammatory Bowel Disease (IBD), including ulcerative colitis and Crohn’s disease.
Chronic systemic diseases and malignancies also increase the sedimentation rate. Long-standing kidney disease, especially end-stage renal disease, can cause elevation due to chronic inflammation. Specific blood or bone marrow cancers, such as multiple myeloma and lymphoma, often result in extremely high ESR values because they produce large amounts of proteins that enhance red cell clumping.
Non-Disease Factors Affecting the Rate
An elevated ESR does not always signify active disease, as several physiological and environmental factors influence the result. The rate tends to increase with age, leading to higher reference values for older adults. Women generally have slightly higher ESR values than men, and pregnancy can also cause a temporary increase.
Anemia, characterized by a reduced number of red blood cells, can artificially raise the ESR. With fewer red cells present, the upward flow of plasma is less restricted, allowing rouleaux to fall more quickly. Lifestyle factors like obesity and smoking have been linked to higher ESR values.
Conversely, some conditions cause a falsely low ESR despite inflammation, complicating interpretation. These include blood disorders like polycythemia, where an excess of red blood cells increases blood viscosity and slows sedimentation. Abnormal red blood cell shapes, such as those in sickle cell disease, impair rouleaux formation, leading to a diminished settling rate. Certain medications, including high-dose aspirin or corticosteroids, may suppress the inflammatory response and lower the ESR.
The Role of ESR in Clinical Diagnosis
The ESR is a non-specific test because it indicates inflammation without identifying the specific location or cause. For this reason, it is rarely used as a standalone diagnostic tool. Instead, it functions as a general screening test when a patient presents with vague symptoms like unexplained fever, joint stiffness, or chronic pain.
The primary clinical application of the ESR is monitoring the activity of known inflammatory conditions, especially chronic autoimmune diseases. In diseases like rheumatoid arthritis, a decrease in the ESR suggests the patient is responding effectively to treatment. A sustained or rising rate may indicate a disease flare or inadequate therapy. Tracking these trends helps clinicians adjust treatment protocols.
Interpreting the result requires consideration of the patient’s complete clinical picture, including a physical examination and other laboratory findings. The ESR is often ordered alongside other inflammation markers, such as C-reactive protein (CRP), which rises and falls more rapidly in response to acute changes. Diagnosis depends on integrating the ESR result with the patient’s symptoms, medical history, and more specific diagnostic tests.