The Erythrocyte Sedimentation Rate (ESR) test, commonly called the “sed rate,” is an inexpensive blood test used to detect and monitor general inflammation. Doctors often order the sed rate when a patient presents with symptoms like unexplained fever, joint pain, or muscle stiffness. The test provides a non-specific indicator of disease activity, suggesting that further investigation is necessary to find the underlying cause.
How the Erythrocyte Sedimentation Rate Test Works
The sed rate test measures the speed at which red blood cells (erythrocytes) settle to the bottom of a tall, thin tube over a period of one hour. In a healthy person, red blood cells generally settle slowly because they have a slight negative charge that causes them to repel each other. The result is measured in millimeters per hour (mm/hr), representing the distance the red blood cells have fallen.
When inflammation is present, the liver produces increased acute-phase proteins, such as fibrinogen and immunoglobulins. These proteins adhere to the red blood cells, neutralizing their negative surface charge. This allows the red blood cells to stick together, forming stacks known as “rouleaux.”
Rouleaux formations are much heavier than single red blood cells, causing them to fall faster under the influence of gravity. The faster the cells settle, the higher the resulting sed rate measurement. Normal ranges vary, but typically for men under 50, the rate is less than 15 mm/hr, and for women under 50, it is less than 20 mm/hr.
Interpreting an Elevated Sed Rate
An elevated sed rate is a non-specific finding, indicating inflammation without identifying the precise cause or location. High results are frequently associated with common acute or chronic infections, as the immune system releases inflammatory markers to fight pathogens. Bacterial infections, for example, often cause a noticeable increase in the sed rate.
Autoimmune conditions are another major cause of persistently elevated results, where the body’s immune system mistakenly attacks its own tissues. Conditions like Rheumatoid Arthritis, Systemic Lupus Erythematosus (Lupus), and Polymyalgia Rheumatica are known to drive the sed rate upward due to widespread systemic inflammation. Monitoring the sed rate can help track the activity and response to treatment for these chronic inflammatory diseases.
Beyond infections and autoimmune disorders, other medical conditions can also influence the reading. Chronic kidney disease, thyroid disorders, and tissue damage from recent trauma or surgery may lead to elevations. Physiological factors, including advanced age, pregnancy, and menstruation, also cause temporary increases. These factors emphasize the need for context when interpreting the result.
When Cancer May Influence Sed Rate Results
Cancer can cause an elevated sed rate by inducing systemic inflammation. Tumor cells and the surrounding immune response release inflammatory signaling molecules called cytokines into the bloodstream. These cytokines stimulate the liver to produce acute-phase proteins, which promote red blood cell clumping and faster sedimentation.
The severity and type of cancer often determine the degree of elevation. Extremely high sed rates, sometimes exceeding 100 mm/hr, are noted in hematologic malignancies like Multiple Myeloma and Lymphoma. In Multiple Myeloma, cancerous plasma cells produce high levels of abnormal antibodies (paraproteins) that significantly enhance rouleaux formation.
In cases of solid tumors, such as advanced breast, colon, or lung cancer, the sed rate may also be elevated, particularly if the cancer has grown large or metastasized to distant sites. A higher tumor burden is often correlated with a greater inflammatory response, leading to a higher sed rate. However, a significant elevation is still only a reflection of the systemic disturbance, not a direct measure of the tumor itself.
Why Sed Rate is Not a Cancer Screening Tool
The sed rate is a non-specific marker and lacks the precision for routine cancer screening in the general population. Many common, non-cancerous conditions cause the sed rate to rise, reducing its usefulness as a standalone diagnostic test for malignancy. Conversely, some individuals with early-stage cancer may have a normal sed rate, indicating a lack of sensitivity for all cancer types.
Due to these limitations, the sed rate is not used to find hidden disease in asymptomatic people. Its value in oncology is limited to serving as a general indicator of illness when a patient presents with unexplained symptoms. A significantly elevated result may prompt a physician to pursue more specific, targeted diagnostic testing, such as imaging scans or biopsies, to identify the underlying cause.