Erythrocyte sedimentation rate (ESR) is a blood test that detects inflammation. It measures how quickly red blood cells, or erythrocytes, settle to the bottom of a test tube. This procedure provides a general indicator of inflammatory activity, guiding healthcare professionals in diagnosis.
Understanding ESR
ESR measures the speed at which red blood cells in a blood sample fall to the bottom of a vertical tube over a specific time, typically one hour. This test functions as a non-specific marker, indicating inflammation or tissue injury. When inflammation occurs, certain proteins increase in the blood, causing red blood cells to clump together. These clumps are denser than individual red blood cells and settle more rapidly. This accelerated settling forms the basis of the ESR measurement. While an elevated ESR points to inflammation, it does not specify the location or cause. Therefore, it serves as a screening tool rather than a definitive diagnostic test.
The ESR Measurement Process
Measuring ESR involves precise laboratory procedures. The process begins with collecting a blood sample, typically from a vein in the arm. The blood must be treated with an anticoagulant to prevent clotting, allowing red blood cells to settle freely.
The Westergren method is widely considered the gold standard for ESR measurement. This method uses a 200-millimeter Westergren tube. Blood is mixed with sodium citrate at a precise ratio before being drawn into the tube up to the zero mark. The tube is then placed vertically for one hour at room temperature.
The Wintrobe method uses a shorter, narrower 100-millimeter tube, often with EDTA as the anticoagulant. Its smaller diameter can lead to lower ESR values compared to Westergren, especially at higher rates. Both methods measure the distance, in millimeters, from the top of the plasma meniscus to the top of the red blood cell column after one hour. Automated ESR analyzers are also common in laboratories, streamlining the process by automatically filling tubes, placing them, and reading the sedimentation rate, enhancing efficiency and reducing human error.
What ESR Results Mean
Interpreting erythrocyte sedimentation rate results involves understanding that an elevated ESR usually indicates the presence of inflammation, infection, or certain diseases within the body. Conditions such as autoimmune diseases, various types of infections, and some cancers can cause a rise in ESR values. However, it is important to remember that ESR is a non-specific test and cannot identify the exact cause of the inflammation.
Normal ESR ranges can vary based on factors such as age and sex. For example, a typical normal range for men under 50 might be 0-15 mm/hr, while for women under 50, it could be 0-20 mm/hr. These reference ranges tend to increase slightly with age. An elevated ESR value suggests that further investigation is needed to determine the underlying cause, and it is considered in conjunction with other clinical findings and additional diagnostic tests. A very low ESR value is uncommon and generally does not carry significant clinical implications.
Variables Affecting ESR Levels
Several factors can influence erythrocyte sedimentation rate levels, independent of disease or inflammatory processes. Physiological variations play a role, with ESR values naturally increasing with age. Women typically have slightly higher ESR values than men, and pregnancy can also cause a significant elevation in ESR.
Technical aspects during the measurement process can also impact the results. If the Westergren tube is not perfectly vertical, even a slight tilt can cause red blood cells to settle more quickly, leading to a falsely elevated reading. Temperature also affects sedimentation; a warmer room temperature can accelerate the rate. The concentration of the anticoagulant used, or the presence of air bubbles in the blood sample column, can similarly alter the accuracy of the measurement.
Certain medical conditions and medications can also affect ESR readings. Severe anemia, where there are fewer red blood cells, can lead to a falsely high ESR because there are fewer cells to impede the settling process. Conversely, conditions like polycythemia, characterized by an abnormally high number of red blood cells, can result in a falsely low ESR. Some medications, such as corticosteroids, which suppress inflammation, can lower ESR values, while others, like certain non-steroidal anti-inflammatory drugs (NSAIDs), might also influence the rate.